fetchmail(1) fetchmail reference manual fetchmail(1)
NAME
fetchmail - fetch mail from a POP, IMAP, ETRN, or ODMR-capable server
SYNOPSIS
fetchmail [option...] [mailserver...]
fetchmailconf
DESCRIPTION
fetchmail is a mail-retrieval and forwarding utility; it fetches mail
from remote mailservers and forwards it to your local (client)
machine's delivery system. You can then handle the retrieved mail
using normal mail user agents such as mutt(1), elm(1) or Mail(1). The
fetchmail utility can be run in a daemon mode to repeatedly poll one or
more systems at a specified interval.
The fetchmail program can gather mail from servers supporting any of
the common mail-retrieval protocols: POP2 (legacy, to be removed from
future release), POP3, IMAP2bis, IMAP4, and IMAP4rev1. It can also use
the ESMTP ETRN extension and ODMR. (The RFCs describing all these pro-
tocols are listed at the end of this manual page.)
While fetchmail is primarily intended to be used over on-demand TCP/IP
links (such as SLIP or PPP connections), it may also be useful as a
message transfer agent for sites which refuse for security reasons to
permit (sender-initiated) SMTP transactions with sendmail.
If fetchmail is used with a POP or an IMAP server, it has two fundamen-
tal modes of operation for each user account from which it retrieves
mail: singledrop- and multidrop-mode. In singledrop-mode, fetchmail
assumes that all messages in the user's account are intended for a sin-
gle recipient. An individual mail message will not be inspected for
recipient information, rather, the identity of the recipient will
either default to the local user currently executing fetchmail, or else
will need to be explicitly specified in the configuration file. Sin-
gledrop-mode is used when the fetchmailrc configuration contains at
most a single local user specification for a given server account.
With multidrop-mode, fetchmail is not able to assume that there is only
a single recipient, but rather that the mail server account actually
contains mail intended for any number of different recipients. There-
fore, fetchmail must attempt to deduce the proper "envelope recipient"
from the mail headers of each message. In this mode of operation,
fetchmail almost resembles an MTA, however it is important to note that
neither the POP nor IMAP protocols were intended for use in this fash-
ion, and hence envelope information is often not directly available.
Instead, fetchmail must resort to a process of informed guess-work in
an attempt to discover the true envelope recipient of a message, unless
the ISP stores the envelope information in some header (not all do).
Even if this information is present in the headers, the process can be
error-prone and is dependent upon the specific mail server used for
mail retrieval. Multidrop-mode is used when more than one local user
is specified for a particular server account in the configuration file.
Note that the forgoing discussion of singledrop- and multidrop-modes
does not apply to the ESMTP ETRN or ODMR retrieval methods, since they
are based upon the SMTP protocol which specifically provides the enve-
lope recipient to fetchmail.
As each message is retrieved, fetchmail normally delivers it via SMTP
to port 25 on the machine it is running on (localhost), just as though
it were being passed in over a normal TCP/IP link. fetchmail provides
the SMTP server with an envelope recipient derived in the manner
described previously. The mail will then be delivered locally via your
system's MDA (Mail Delivery Agent, usually sendmail(8) but your system
may use a different one such as smail, mmdf, exim, postfix, or qmail).
All the delivery-control mechanisms (such as .forward files) normally
available through your system MDA and local delivery agents will there-
fore work automatically.
If no port 25 listener is available, but your fetchmail configuration
was told about a reliable local MDA, it will use that MDA for local
delivery instead.
If the program fetchmailconf is available, it will assist you in set-
ting up and editing a fetchmailrc configuration. It runs under the X
window system and requires that the language Python and the Tk toolkit
be present on your system. If you are first setting up fetchmail for
single-user mode, it is recommended that you use Novice mode. Expert
mode provides complete control of fetchmail configuration, including
the multidrop features. In either case, the 'Autoprobe' button will
tell you the most capable protocol a given mailserver supports, and
warn you of potential problems with that server.
GENERAL OPERATION
The behavior of fetchmail is controlled by command-line options and a
run control file, ~/.fetchmailrc, the syntax of which we describe in a
later section (this file is what the fetchmailconf program edits).
Command-line options override ~/.fetchmailrc declarations.
Each server name that you specify following the options on the command
line will be queried. If you don't specify any servers on the command
line, each 'poll' entry in your ~/.fetchmailrc file will be queried.
To facilitate the use of fetchmail in scripts and pipelines, it returns
an appropriate exit code upon termination -- see EXIT CODES below.
The following options modify the behavior of fetchmail. It is seldom
necessary to specify any of these once you have a working .fetchmailrc
file set up.
Almost all options have a corresponding keyword which can be used to
declare them in a .fetchmailrc file.
Some special options are not covered here, but are documented instead
in sections on AUTHENTICATION and DAEMON MODE which follow.
General Options
-V | --version
Displays the version information for your copy of fetchmail. No
mail fetch is performed. Instead, for each server specified,
all the option information that would be computed if fetchmail
were connecting to that server is displayed. Any non-printables
in passwords or other string names are shown as backslashed C-
like escape sequences. This option is useful for verifying that
your options are set the way you want them.
-c | --check
Return a status code to indicate whether there is mail waiting,
without actually fetching or deleting mail (see EXIT CODES
below). This option turns off daemon mode (in which it would be
useless). It doesn't play well with queries to multiple sites,
and doesn't work with ETRN or ODMR. It will return a false pos-
itive if you leave read but undeleted mail in your server mail-
box and your fetch protocol can't tell kept messages from new
ones. This means it will work with IMAP, not work with POP2,
and may occasionally flake out under POP3.
-s | --silent
Silent mode. Suppresses all progress/status messages that are
normally echoed to standard output during a fetch (but does not
suppress actual error messages). The --verbose option overrides
this.
-v | --verbose
Verbose mode. All control messages passed between fetchmail and
the mailserver are echoed to stdout. Overrides --silent. Dou-
bling this option (-v -v) causes extra diagnostic information to
be printed.
Disposal Options
-a | --all | (since v6.3.3) --fetchall
(Keyword: fetchall, since v3.0) Retrieve both old (seen) and new
messages from the mailserver. The default is to fetch only mes-
sages the server has not marked seen. Under POP3, this option
also forces the use of RETR rather than TOP. Note that POP2
retrieval behaves as though --all is always on (see RETRIEVAL
FAILURE MODES below) and this option does not work with ETRN or
ODMR. While the -a and --all command-line and fetchall rcfile
options have been supported for a long time, the --fetchall com-
mand-line option was added in v6.3.3.
-k | --keep
(Keyword: keep) Keep retrieved messages on the remote
mailserver. Normally, messages are deleted from the folder on
the mailserver after they have been retrieved. Specifying the
keep option causes retrieved messages to remain in your folder
on the mailserver. This option does not work with ETRN or ODMR.
If used with POP3, it is recommended to also specify the --uidl
option or uidl keyword.
-K | --nokeep
(Keyword: nokeep) Delete retrieved messages from the remote
mailserver. This option forces retrieved mail to be deleted.
It may be useful if you have specified a default of keep in your
.fetchmailrc. This option is forced on with ETRN and ODMR.
-F | --flush
POP3/IMAP only. This is a dangerous option and can cause mail
loss when used improperly. It deletes old (seen) messages from
the mailserver before retrieving new messages. Warning: This
can cause mail loss if you check your mail with other clients
than fetchmail, and cause fetchmail to delete a message it had
never fetched before. It can also cause mail loss if the mail
server marks the message seen after retrieval (IMAP2 servers).
You should probably not use this option in your configuration
file. If you use it with POP3, you must use the 'uidl' option.
What you probably want is the default setting: if you don't
specify '-k', then fetchmail will automatically delete messages
after successful delivery.
--limitflush
POP3/IMAP only, since version 6.3.0. Delete oversized messages
from the mailserver before retrieving new messages. The size
limit should be separately specified with the --limit option.
This option does not work with ETRN or ODMR.
Protocol and Query Options
-p <proto> | --proto <proto> | --protocol <proto>
(Keyword: proto[col]) Specify the protocol to use when communi-
cating with the remote mailserver. If no protocol is specified,
the default is AUTO. proto may be one of the following:
AUTO Tries IMAP, POP3, and POP2 (skipping any of these for
which support has not been compiled in).
POP2 Post Office Protocol 2 (legacy, to be removed from future
release)
POP3 Post Office Protocol 3
APOP Use POP3 with old-fashioned MD5-challenge authentication.
Considered not resistant to man-in-the-middle attacks.
RPOP Use POP3 with RPOP authentication.
KPOP Use POP3 with Kerberos V4 authentication on port 1109.
SDPS Use POP3 with Demon Internet's SDPS extensions.
IMAP IMAP2bis, IMAP4, or IMAP4rev1 (fetchmail automatically
detects their capabilities).
ETRN Use the ESMTP ETRN option.
ODMR Use the the On-Demand Mail Relay ESMTP profile.
All these alternatives work in basically the same way (communicating
with standard server daemons to fetch mail already delivered to a mail-
box on the server) except ETRN and ODMR. The ETRN mode allows you to
ask a compliant ESMTP server (such as BSD sendmail at release 8.8.0 or
higher) to immediately open a sender-SMTP connection to your client
machine and begin forwarding any items addressed to your client machine
in the server's queue of undelivered mail. The ODMR mode requires an
ODMR-capable server and works similarly to ETRN, except that it does
not require the client machine to have a static DNS.
-U | --uidl
(Keyword: uidl) Force UIDL use (effective only with POP3).
Force client-side tracking of 'newness' of messages (UIDL stands
for "unique ID listing" and is described in RFC1939). Use with
'keep' to use a mailbox as a baby news drop for a group of
users. The fact that seen messages are skipped is logged, unless
error logging is done through syslog while running in daemon
mode. Note that fetchmail may automatically enable this option
depending on upstream server capabilities. Note also that this
option may be removed and forced enabled in a future fetchmail
version. See also: --idfile.
--idle (since 6.3.3)
(Keyword: idle, since before 6.0.0) Enable IDLE use (effective
only with IMAP). Note that this works with only one folder at a
given time. While the idle rcfile keyword had been supported
for a long time, the --idle command-line option was added in
version 6.3.3. IDLE use means that fetchmail tells the IMAP
server to send notice of new messages, so they can be retrieved
sooner than would be possible with regular polls.
-P <portnumber> | --service <servicename>
(Keyword: service) Since version 6.3.0. The service option per-
mits you to specify a service name to connect to. You can spec-
ify a decimal port number here, if your services database lacks
the required service-port assignments. See the FAQ item R12 and
the --ssl documentation for details. This replaces the older
--port option.
--port <portnumber>
(Keyword: port) Obsolete version of --service that does not take
service names. Note: this option may be removed from a future
version.
--principal <principal>
(Keyword: principal) The principal option permits you to specify
a service principal for mutual authentication. This is applica-
ble to POP3 or IMAP with Kerberos authentication.
-t <seconds> | --timeout <seconds>
(Keyword: timeout) The timeout option allows you to set a
server-nonresponse timeout in seconds. If a mailserver does not
send a greeting message or respond to commands for the given
number of seconds, fetchmail will hang up on it. Without such a
timeout fetchmail might hang indefinitely trying to fetch mail
from a down host. This would be particularly annoying for a
fetchmail running in the background. There is a default timeout
which fetchmail -V will report. If a given connection receives
too many timeouts in succession, fetchmail will consider it
wedged and stop retrying. The calling user will be notified by
email if this happens.
--plugin <command>
(Keyword: plugin) The plugin option allows you to use an exter-
nal program to establish the TCP connection. This is useful if
you want to use SSL, ssh, or need some special firewalling set-
up. The program will be looked up in $PATH and can optionally
be passed the hostname and port as arguments using "%h" and "%p"
respectively (note that the interpolation logic is rather primi-
tive, and these token must be bounded by whitespace or beginning
of string or end of string). Fetchmail will write to the plug-
in's stdin and read from the plugin's stdout.
--plugout <command>
(Keyword: plugout) Identical to the plugin option above, but
this one is used for the SMTP connections (which will probably
not need it, so it has been separated from plugin).
-r <name> | --folder <name>
(Keyword: folder[s]) Causes a specified non-default mail folder
on the mailserver (or comma-separated list of folders) to be
retrieved. The syntax of the folder name is server-dependent.
This option is not available under POP3, ETRN, or ODMR.
--tracepolls
(Keyword: tracepolls) Tell fetchmail to poll trace information
in the form 'polling %s account %s' and 'folder %s' to the
Received line it generates, where the %s parts are replaced by
the user's remote name, the poll label, and the folder (mailbox)
where available (the Received header also normally includes the
server's true name). This can be used to facilitate mail fil-
tering based on the account it is being received from. The
folder information is written only since version 6.3.4.
--ssl (Keyword: ssl) Causes the connection to the mail server to be
encrypted via SSL. Connect to the server using the specified
base protocol over a connection secured by SSL. This option
defeats TLS negotiation. Use --sslcertck to validate the cer-
tificates presented by the server.
Note that fetchmail may still try to negotiate TLS even if this
option is not given. You can use the --sslproto option to defeat
this behavior or tell fetchmail to negotiate a particular SSL
protocol.
If no port is specified, the connection is attempted to the well
known port of the SSL version of the base protocol. This is
generally a different port than the port used by the base proto-
col. For IMAP, this is port 143 for the clear protocol and port
993 for the SSL secured protocol, for POP3, it is port 110 for
the clear text and port 995 for the encrypted variant.
If your system lacks the corresponding entries from /etc/ser-
vices, see the --service option and specify the numeric port
number as given in the previous paragraph (unless your ISP had
directed you to different ports, which is uncommon however).
--sslcert <name>
(Keyword: sslcert) Specifies the file name of the client side
public SSL certificate. Some SSL encrypted servers may require
client side keys and certificates for authentication. In most
cases, this is optional. This specifies the location of the
public key certificate to be presented to the server at the time
the SSL session is established. It is not required (but may be
provided) if the server does not require it. Some servers may
require it, some servers may request it but not require it, and
some servers may not request it at all. It may be the same file
as the private key (combined key and certificate file) but this
is not recommended.
NOTE: If you use client authentication, the user name is fetched
from the certificate's CommonName and overrides the name set
with --user.
--sslkey <name>
(Keyword: sslkey) Specifies the file name of the client side
private SSL key. Some SSL encrypted servers may require client
side keys and certificates for authentication. In most cases,
this is optional. This specifies the location of the private
key used to sign transactions with the server at the time the
SSL session is established. It is not required (but may be pro-
vided) if the server does not require it. Some servers may
require it, some servers may request it but not require it, and
some servers may not request it at all. It may be the same file
as the public key (combined key and certificate file) but this
is not recommended. If a password is required to unlock the
key, it will be prompted for at the time just prior to estab-
lishing the session to the server. This can cause some compli-
cations in daemon mode.
--sslproto <name>
(Keyword: sslproto) Forces an SSL or TLS protocol. Possible val-
ues are 'SSL2', 'SSL3', 'SSL23', and 'TLS1'. Try this if the
default handshake does not work for your server. Use this option
with 'TLS1' to enforce a TLS connection. To defeat opportunistic
TLSv1 negotiation when the server advertises STARTTLS or STLS,
use ''. This option, even if the argument is the empty string,
will also suppress the diagnostic 'SERVER: opportunistic upgrade
to TLS.' message in verbose mode. The default is to try appro-
priate protocols depending on context.
--sslcertck
(Keyword: sslcertck) Causes fetchmail to strictly check the
server certificate against a set of local trusted certificates
(see the sslcertpath option). If the server certificate cannot
be obtained or is not signed by one of the trusted ones
(directly or indirectly), the SSL connection will fail, regard-
less of the sslfingerprint option. Note that CRL are only sup-
ported in OpenSSL 0.9.7 and newer! Your system clock should also
be reasonably accurate when using this option.
Note that this optional behavior may become default behavior in
future fetchmail versions.
--sslcertpath <directory>
(Keyword: sslcertpath) Sets the directory fetchmail uses to look
up local certificates. The default is your OpenSSL default one.
The directory must be hashed as OpenSSL expects it - every time
you add or modify a certificate in the directory, you need to
use the c_rehash tool (which comes with OpenSSL in the tools/
subdirectory).
--sslcommonname <common name>
(Keyword: sslcommonname) Use of this option is discouraged.
Before using it, contact the administrator of your upstream
server and ask for a proper SSL certificate to be used. If that
cannot be attained, this option can be used to specify the name
(CommonName) that fetchmail expects on the server certificate.
A correctly configured server will have this set to the hostname
by which it is reached, and by default fetchmail will expect as
much. Use this option when the CommonName is set to some other
value, to avoid the "Server CommonName mismatch" warning, and
only if the upstream server can't be made to use proper certifi-
cates.
--sslfingerprint <fingerprint>
(Keyword: sslfingerprint) Specify the fingerprint of the server
key (an MD5 hash of the key) in hexadecimal notation with colons
separating groups of two digits. The letter hex digits must be
in upper case. This is the default format OpenSSL uses, and the
one fetchmail uses to report the fingerprint when an SSL connec-
tion is established. When this is specified, fetchmail will com-
pare the server key fingerprint with the given one, and the con-
nection will fail if they do not match regardless of the
sslcertck setting. The connection will also fail if fetchmail
cannot obtain an SSL certificate from the server. This can be
used to prevent man-in-the-middle attacks, but the finger print
from the server needs to be obtained or verified over a secure
channel, and certainly not over the same Internet connection
that fetchmail would use.
Using this option will prevent printing certificate verification
errors as long as --sslcertck is unset.
To obtain the fingerprint of a certificate stored in the file
cert.pem, try:
openssl x509 -in cert.pem -noout -md5 -fingerprint
For details, see x509(1ssl).
Delivery Control Options
-S <hosts> | --smtphost <hosts>
(Keyword: smtp[host]) Specify a hunt list of hosts to forward
mail to (one or more hostnames, comma-separated). Hosts are
tried in list order; the first one that is up becomes the for-
warding target for the current run. If this option is not spec-
ified, 'localhost' is used as the default. Each hostname may
have a port number following the host name. The port number is
separated from the host name by a slash; the default port is
"smtp". If you specify an absolute path name (beginning with a
/), it will be interpreted as the name of a UNIX socket accept-
ing LMTP connections (such as is supported by the Cyrus IMAP
daemon) Example:
--smtphost server1,server2/2525,server3,/var/imap/socket/lmtp
This option can be used with ODMR, and will make fetchmail a
relay between the ODMR server and SMTP or LMTP receiver.
--fetchdomains <hosts>
(Keyword: fetchdomains) In ETRN or ODMR mode, this option speci-
fies the list of domains the server should ship mail for once
the connection is turned around. The default is the FQDN of the
machine running fetchmail.
-D <domain> | --smtpaddress <domain>
(Keyword: smtpaddress) Specify the domain to be appended to
addresses in RCPT TO lines shipped to SMTP. When this is not
specified, the name of the SMTP server (as specified by --smt-
phost) is used for SMTP/LMTP and 'localhost' is used for UNIX
socket/BSMTP.
--smtpname <user@domain>
(Keyword: smtpname) Specify the domain and user to be put in
RCPT TO lines shipped to SMTP. The default user is the current
local user.
-Z <nnn> | --antispam <nnn[, nnn]...>
(Keyword: antispam) Specifies the list of numeric SMTP errors
that are to be interpreted as a spam-block response from the
listener. A value of -1 disables this option. For the command-
line option, the list values should be comma-separated.
-m <command> | --mda <command>
(Keyword: mda) You can force mail to be passed to an MDA
directly (rather than forwarded to port 25) with the --mda or -m
option.
To avoid losing mail, use this option only with MDAs like mail-
drop or MTAs like sendmail that return a nonzero status on disk-
full and other resource-exhaustion errors; the nonzero status
tells fetchmail that delivery failed and prevents the message
from being deleted off the server.
If fetchmail is running as root, it sets its user id to that of
the target user while delivering mail through an MDA. Some pos-
sible MDAs are "/usr/sbin/sendmail -i -f %F -- %T" (Note: some
several older or vendor sendmail versions mistake -- for an
address, rather than an indicator to mark the end of the option
arguments), "/usr/bin/deliver" and "/usr/bin/maildrop -d %T".
Local delivery addresses will be inserted into the MDA command
wherever you place a %T; the mail message's From address will be
inserted where you place an %F.
DO NOT ENCLOSE THE %F OR %T STRING IN SINGLE QUOTES! For both
%T and %F, fetchmail encloses the addresses in single quotes
('), after removing any single quotes they may contain, before
the MDA command is passed to the shell.
Do NOT use an MDA invocation that dispatches on the contents of
To/Cc/Bcc, like "sendmail -i -t" or "qmail-inject", it will cre-
ate mail loops and bring the just wrath of many postmasters down
upon your head. This is one of the most frequent configuration
errors!
Also, do not try to combine multidrop mode with an MDA such as
maildrop that can only accept one address, unless your upstream
stores one copy of the message per recipient and transports the
envelope recipient in a header; you will lose mail.
The well-known procmail(1) package is very hard to configure
properly, it has a very nasty "fall through to the next rule"
behavior on delivery errors (even temporary ones, such as out of
disk space if another user's mail daemon copies the mailbox
around to purge old messages), so your mail will end up in the
wrong mailbox sooner or later. The proper procmail configuration
is outside the scope of this document. Using maildrop(1) is usu-
ally much easier, and many users find the filter syntax used by
maildrop easier to understand.
Finally, we strongly advise that you do not use qmail-inject.
The command line interface is non-standard without providing
benefits for typical use, and fetchmail makes no attempts to
accomodate qmail-inject's deviations from the standard. Some of
qmail-inject's command-line and environment options are actually
dangerous and can cause broken threads, non-detected duplicate
messages and forwarding loops.
--lmtp (Keyword: lmtp) Cause delivery via LMTP (Local Mail Transfer
Protocol). A service host and port must be explicitly specified
on each host in the smtphost hunt list (see above) if this
option is selected; the default port 25 will (in accordance with
RFC 2033) not be accepted.
--bsmtp <filename>
(keyword: bsmtp) Append fetched mail to a BSMTP file. This sim-
ply contains the SMTP commands that would normally be generated
by fetchmail when passing mail to an SMTP listener daemon. An
argument of '-' causes the mail to be written to standard out-
put. Note that fetchmail's reconstruction of MAIL FROM and RCPT
TO lines is not guaranteed correct; the caveats discussed under
THE USE AND ABUSE OF MULTIDROP MAILBOXES below apply.
Resource Limit Control Options
-l <maxbytes> | --limit <maxbytes>
(Keyword: limit) Takes a maximum octet size argument, where 0 is
the default and also the special value designating "no limit".
If nonzero, messages larger than this size will not be fetched
and will be left on the server (in foreground sessions, the
progress messages will note that they are "oversized"). If the
fetch protocol permits (in particular, under IMAP or POP3 with-
out the fetchall option) the message will not be marked seen.
An explicit --limit of 0 overrides any limits set in your run
control file. This option is intended for those needing to
strictly control fetch time due to expensive and variable phone
rates.
Combined with --limitflush, it can be used to delete oversized
messages waiting on a server. In daemon mode, oversize notifi-
cations are mailed to the calling user (see the --warnings
option). This option does not work with ETRN or ODMR.
-w <interval> | --warnings <interval>
(Keyword: warnings) Takes an interval in seconds. When you call
fetchmail with a 'limit' option in daemon mode, this controls
the interval at which warnings about oversized messages are
mailed to the calling user (or the user specified by the 'post-
master' option). One such notification is always mailed at the
end of the the first poll that the oversized message is
detected. Thereafter, re-notification is suppressed until after
the warning interval elapses (it will take place at the end of
the first following poll).
-b <count> | --batchlimit <count>
(Keyword: batchlimit) Specify the maximum number of messages
that will be shipped to an SMTP listener before the connection
is deliberately torn down and rebuilt (defaults to 0, meaning no
limit). An explicit --batchlimit of 0 overrides any limits set
in your run control file. While sendmail(8) normally initiates
delivery of a message immediately after receiving the message
terminator, some SMTP listeners are not so prompt. MTAs like
smail(8) may wait till the delivery socket is shut down to
deliver. This may produce annoying delays when fetchmail is
processing very large batches. Setting the batch limit to some
nonzero size will prevent these delays. This option does not
work with ETRN or ODMR.
-B <number> | --fetchlimit <number>
(Keyword: fetchlimit) Limit the number of messages accepted from
a given server in a single poll. By default there is no limit.
An explicit --fetchlimit of 0 overrides any limits set in your
run control file. This option does not work with ETRN or ODMR.
--fetchsizelimit <number>
(Keyword: fetchsizelimit) Limit the number of sizes of messages
accepted from a given server in a single transaction. This
option is useful in reducing the delay in downloading the first
mail when there are too many mails in the mailbox. By default,
the limit is 100. If set to 0, sizes of all messages are down-
loaded at the start. This option does not work with ETRN or
ODMR. For POP3, the only valid non-zero value is 1.
--fastuidl <number>
(Keyword: fastuidl) Do a binary instead of linear search for the
first unseen UID. Binary search avoids downloading the UIDs of
all mails. This saves time (especially in daemon mode) where
downloading the same set of UIDs in each poll is a waste of
bandwidth. The number 'n' indicates how rarely a linear search
should be done. In daemon mode, linear search is used once fol-
lowed by binary searches in 'n-1' polls if 'n' is greater than
1; binary search is always used if 'n' is 1; linear search is
always used if 'n' is 0. In non-daemon mode, binary search is
used if 'n' is 1; otherwise linear search is used. The default
value of 'n' is 4. This option works with POP3 only.
-e <count> | --expunge <count>
(keyword: expunge) Arrange for deletions to be made final after
a given number of messages. Under POP2 or POP3, fetchmail can-
not make deletions final without sending QUIT and ending the
session -- with this option on, fetchmail will break a long mail
retrieval session into multiple sub-sessions, sending QUIT after
each sub-session. This is a good defense against line drops on
POP3 servers. Under IMAP, fetchmail normally issues an EXPUNGE
command after each deletion in order to force the deletion to be
done immediately. This is safest when your connection to the
server is flaky and expensive, as it avoids resending duplicate
mail after a line hit. However, on large mailboxes the overhead
of re-indexing after every message can slam the server pretty
hard, so if your connection is reliable it is good to do
expunges less frequently. Also note that some servers enforce a
delay of a few seconds after each quit, so fetchmail may not be
able to get back in immediately after an expunge -- you may see
"lock busy" errors if this happens. If you specify this option
to an integer N, it tells fetchmail to only issue expunges on
every Nth delete. An argument of zero suppresses expunges
entirely (so no expunges at all will be done until the end of
run). This option does not work with ETRN or ODMR.
Authentication Options
-u <name> | --user <name> | --username <name>
(Keyword: user[name]) Specifies the user identification to be
used when logging in to the mailserver. The appropriate user
identification is both server and user-dependent. The default
is your login name on the client machine that is running fetch-
mail. See USER AUTHENTICATION below for a complete description.
-I <specification> | --interface <specification>
(Keyword: interface) Require that a specific interface device be
up and have a specific local or remote IPv4 (IPv6 is not sup-
ported by this option yet) address (or range) before polling.
Frequently fetchmail is used over a transient point-to-point
TCP/IP link established directly to a mailserver via SLIP or
PPP. That is a relatively secure channel. But when other
TCP/IP routes to the mailserver exist (e.g. when the link is
connected to an alternate ISP), your username and password may
be vulnerable to snooping (especially when daemon mode automati-
cally polls for mail, shipping a clear password over the net at
predictable intervals). The --interface option may be used to
prevent this. When the specified link is not up or is not con-
nected to a matching IP address, polling will be skipped. The
format is:
interface/iii.iii.iii.iii[/mmm.mmm.mmm.mmm]
The field before the first slash is the interface name (i.e.
sl0, ppp0 etc.). The field before the second slash is the
acceptable IP address. The field after the second slash is a
mask which specifies a range of IP addresses to accept. If no
mask is present 255.255.255.255 is assumed (i.e. an exact
match). This option is currently only supported under Linux and
FreeBSD. Please see the monitor section for below for FreeBSD
specific information.
Note that this option may be removed from a future fetchmail
version.
-M <interface> | --monitor <interface>
(Keyword: monitor) Daemon mode can cause transient links which
are automatically taken down after a period of inactivity (e.g.
PPP links) to remain up indefinitely. This option identifies a
system TCP/IP interface to be monitored for activity. After
each poll interval, if the link is up but no other activity has
occurred on the link, then the poll will be skipped. However,
when fetchmail is woken up by a signal, the monitor check is
skipped and the poll goes through unconditionally. This option
is currently only supported under Linux and FreeBSD. For the
monitor and interface options to work for non root users under
FreeBSD, the fetchmail binary must be installed SGID kmem. This
would be a security hole, but fetchmail runs with the effective
GID set to that of the kmem group only when interface data is
being collected.
Note that this option may be removed from a future fetchmail
version.
--auth <type>
(Keyword: auth[enticate]) This option permits you to specify an
authentication type (see USER AUTHENTICATION below for details).
The possible values are any, password, kerberos_v5, kerberos
(or, for excruciating exactness, kerberos_v4), gssapi, cram-md5,
otp, ntlm, msn (only for POP3), external (only IMAP) and ssh.
When any (the default) is specified, fetchmail tries first meth-
ods that don't require a password (EXTERNAL, GSSAPI, KER-
BEROS IV, KERBEROS 5); then it looks for methods that mask your
password (CRAM-MD5, X-OTP - note that NTLM and MSN are not auto-
probed for POP3 and MSN is only supported for POP3); and only if
the server doesn't support any of those will it ship your pass-
word en clair. Other values may be used to force various
authentication methods (ssh suppresses authentication and is
thus useful for IMAP PREAUTH). (external suppresses authentica-
tion and is thus useful for IMAP EXTERNAL). Any value other
than password, cram-md5, ntlm, msn or otp suppresses fetchmail's
normal inquiry for a password. Specify ssh when you are using
an end-to-end secure connection such as an ssh tunnel; specify
external when you use TLS with client authentication and specify
gssapi or kerberos_v4 if you are using a protocol variant that
employs GSSAPI or K4. Choosing KPOP protocol automatically
selects Kerberos authentication. This option does not work with
ETRN.
Miscellaneous Options
-f <pathname> | --fetchmailrc <pathname>
Specify a non-default name for the ~/.fetchmailrc run control
file. The pathname argument must be either "-" (a single dash,
meaning to read the configuration from standard input) or a
filename. Unless the --version option is also on, a named file
argument must have permissions no more open than 0700
(u=rwx,g=,o=) or else be /dev/null.
-i <pathname> | --idfile <pathname>
(Keyword: idfile) Specify an alternate name for the .fetchids
file used to save message UIDs. NOTE: since fetchmail 6.3.0,
write access to the directory containing the idfile is required,
as fetchmail writes a temporary file and renames it into the
place of the real idfile only if the temporary file has been
written successfully. This avoids the truncation of idfiles when
running out of disk space.
--pidfile <pathname>
(Keyword: pidfile; since fetchmail v6.3.4) Override the default
location of the PID file. Default: see "ENVIRONMENT" below.
-n | --norewrite
(Keyword: no rewrite) Normally, fetchmail edits RFC-822 address
headers (To, From, Cc, Bcc, and Reply-To) in fetched mail so
that any mail IDs local to the server are expanded to full
addresses (@ and the mailserver hostname are appended). This
enables replies on the client to get addressed correctly (other-
wise your mailer might think they should be addressed to local
users on the client machine!). This option disables the re-
write. (This option is provided to pacify people who are para-
noid about having an MTA edit mail headers and want to know they
can prevent it, but it is generally not a good idea to actually
turn off rewrite.) When using ETRN or ODMR, the rewrite option
is ineffective.
-E <line> | --envelope <line>
(Keyword: envelope; Multidrop only)
In the configuration file, an enhanced syntax is used:
envelope [<count>] <line>
This option changes the header fetchmail assumes will carry a
copy of the mail's envelope address. Normally this is 'X-Enve-
lope-To'. Other typically found headers to carry envelope infor-
mation are 'X-Original-To' and 'Delivered-To'. Now, since these
headers are not standardized, practice varies. See the discus-
sion of multidrop address handling below. As a special case,
'envelope "Received"' enables parsing of sendmail-style Received
lines. This is the default, but discouraged because it is not
fully reliable.
Note that fetchmail expects the Received-line to be in a spe-
cific format: It must contain "by host for address", where host
must match one of the mailserver names that fetchmail recognizes
for the account in question.
The optional count argument (only available in the configuration
file) determines how many header lines of this kind are skipped.
A count of 1 means: skip the first, take the second. A count of
2 means: skip the first and second, take the third, and so on.
-Q <prefix> | --qvirtual <prefix>
(Keyword: qvirtual; Multidrop only) The string prefix assigned
to this option will be removed from the user name found in the
header specified with the envelope option (before doing mul-
tidrop name mapping or localdomain checking, if either is appli-
cable). This option is useful if you are using fetchmail to col-
lect the mail for an entire domain and your ISP (or your mail
redirection provider) is using qmail. One of the basic features
of qmail is the
'Delivered-To:'
message header. Whenever qmail delivers a message to a local
mailbox it puts the username and hostname of the envelope recip-
ient on this line. The major reason for this is to prevent mail
loops. To set up qmail to batch mail for a disconnected site
the ISP-mailhost will have normally put that site in its 'Virtu-
alhosts' control file so it will add a prefix to all mail
addresses for this site. This results in mail sent to 'user-
name@userhost.userdom.dom.com' having a 'Delivered-To:' line of
the form:
Delivered-To: mbox-userstr-username@userhost.example.com
The ISP can make the 'mbox-userstr-' prefix anything they choose
but a string matching the user host name is likely. By using
the option 'envelope Delivered-To:' you can make fetchmail reli-
ably identify the original envelope recipient, but you have to
strip the 'mbox-userstr-' prefix to deliver to the correct user.
This is what this option is for.
--configdump
Parse the ~/.fetchmailrc file, interpret any command-line
options specified, and dump a configuration report to standard
output. The configuration report is a data structure assignment
in the language Python. This option is meant to be used with an
interactive ~/.fetchmailrc editor like fetchmailconf, written in
Python.
Removed Options
-T | --netsec
Removed before version 6.3.0, the required underlying inet6_apps
library had been discontinued and is no longer available.
USER AUTHENTICATION AND ENCRYPTION
All modes except ETRN require authentication of the client to the
server. Normal user authentication in fetchmail is very much like the
authentication mechanism of ftp(1). The correct user-id and password
depend upon the underlying security system at the mailserver.
If the mailserver is a Unix machine on which you have an ordinary user
account, your regular login name and password are used with fetchmail.
If you use the same login name on both the server and the client
machines, you needn't worry about specifying a user-id with the -u
option -- the default behavior is to use your login name on the client
machine as the user-id on the server machine. If you use a different
login name on the server machine, specify that login name with the -u
option. e.g. if your login name is 'jsmith' on a machine named 'mail-
grunt', you would start fetchmail as follows:
fetchmail -u jsmith mailgrunt
The default behavior of fetchmail is to prompt you for your mailserver
password before the connection is established. This is the safest way
to use fetchmail and ensures that your password will not be compro-
mised. You may also specify your password in your ~/.fetchmailrc file.
This is convenient when using fetchmail in daemon mode or with scripts.
Using netrc files
If you do not specify a password, and fetchmail cannot extract one from
your ~/.fetchmailrc file, it will look for a ~/.netrc file in your home
directory before requesting one interactively; if an entry matching the
mailserver is found in that file, the password will be used. Fetchmail
first looks for a match on poll name; if it finds none, it checks for a
match on via name. See the ftp(1) man page for details of the syntax
of the ~/.netrc file. To show a practical example, a .netrc might look
like this:
machine hermes.example.org
login joe
password topsecret
You can repeat this block with different user information if you need
to provide more than one password.
This feature may allow you to avoid duplicating password information in
more than one file.
On mailservers that do not provide ordinary user accounts, your user-id
and password are usually assigned by the server administrator when you
apply for a mailbox on the server. Contact your server administrator
if you don't know the correct user-id and password for your mailbox
account.
POP3 VARIANTS
Early versions of POP3 (RFC1081, RFC1225) supported a crude form of
independent authentication using the rhosts file on the mailserver
side. Under this RPOP variant, a fixed per-user ID equivalent to a
password was sent in clear over a link to a reserved port, with the
command RPOP rather than PASS to alert the server that it should do
special checking. RPOP is supported by fetchmail (you can specify
'protocol RPOP' to have the program send 'RPOP' rather than 'PASS') but
its use is strongly discouraged, and support will be removed from a
future fetchmail version. This facility was vulnerable to spoofing and
was withdrawn in RFC1460.
RFC1460 introduced APOP authentication. In this variant of POP3, you
register an APOP password on your server host (on some servers, the
program to do this is called popauth(8)). You put the same password in
your ~/.fetchmailrc file. Each time fetchmail logs in, it sends an MD5
hash of your password and the server greeting time to the server, which
can verify it by checking its authorization database.
Note that APOP is no longer considered resistant against man-in-the-
middle attacks.
RETR or TOP
fetchmail makes some efforts to make the server believe messages had
not been retrieved, by using the TOP command with a large number of
lines when possible. TOP is a command that retrieves the full header
and a fetchmail-specified amount of body lines. It is optional and
therefore not implemented by all servers, and some are known to imple-
ment it improperly. On many servers however, the RETR command which
retrieves the full message with header and body, sets the "seen" flag
(for instance, in a web interface), whereas the TOP command does not do
that.
fetchmail will always use the RETR command if "fetchall" is set.
fetchmail will also use the RETR command if "keep" is set and "uidl" is
unset. Finally, fetchmail will use the RETR command on Maillennium
POP3/PROXY servers (used by Comcast) to avoid a deliberate TOP misin-
terpretation in this server that causes message corruption.
In all other cases, fetchmail will use the TOP command. This implies
that in "keep" setups, "uidl" must be set if "TOP" is desired.
Note that this description is true for the current version of fetch-
mail, but the behavior may change in future versions. In particular,
fetchmail may prefer the RETR command because the TOP command causes
much grief on some servers and is only optional.
ALTERNATE AUTHENTICATION FORMS
If your fetchmail was built with Kerberos support and you specify Ker-
beros authentication (either with --auth or the .fetchmailrc option
authenticate kerberos_v4) it will try to get a Kerberos ticket from the
mailserver at the start of each query. Note: if either the pollname or
via name is 'hesiod', fetchmail will try to use Hesiod to look up the
mailserver.
If you use POP3 or IMAP with GSSAPI authentication, fetchmail will
expect the server to have RFC1731- or RFC1734-conforming GSSAPI capa-
bility, and will use it. Currently this has only been tested over Ker-
beros V, so you're expected to already have a ticket-granting ticket.
You may pass a username different from your principal name using the
standard --user command or by the .fetchmailrc option user.
If your IMAP daemon returns the PREAUTH response in its greeting line,
fetchmail will notice this and skip the normal authentication step.
This can be useful, e.g. if you start imapd explicitly using ssh. In
this case you can declare the authentication value 'ssh' on that site
entry to stop .fetchmail from asking you for a password when it starts
up.
If you use client authentication with TLS1 and your IMAP daemon returns
the AUTH=EXTERNAL response, fetchmail will notice this and will use the
authentication shortcut and will not send the passphrase. In this case
you can declare the authentication value 'external'
on that site to stop fetchmail from asking you for a password when it
starts up.
If you are using POP3, and the server issues a one-time-password chal-
lenge conforming to RFC1938, fetchmail will use your password as a pass
phrase to generate the required response. This avoids sending secrets
over the net unencrypted.
Compuserve's RPA authentication is supported. If you compile in the
support, fetchmail will try to perform an RPA pass-phrase authentica-
tion instead of sending over the password en clair if it detects "@com-
puserve.com" in the hostname.
If you are using IMAP, Microsoft's NTLM authentication (used by
Microsoft Exchange) is supported. If you compile in the support, fetch-
mail will try to perform an NTLM authentication (instead of sending
over the password en clair) whenever the server returns AUTH=NTLM in
its capability response. Specify a user option value that looks like
'user@domain': the part to the left of the @ will be passed as the
username and the part to the right as the NTLM domain.
Secure Socket Layers (SSL) and Transport Layer Security (TLS)
You can access SSL encrypted services by specifying the --ssl option.
You can also do this using the "ssl" user option in the .fetchmailrc
file. With SSL encryption enabled, queries are initiated over a connec-
tion after negotiating an SSL session, and the connection fails if SSL
cannot be negotiated. Some services, such as POP3 and IMAP, have dif-
ferent well known ports defined for the SSL encrypted services. The
encrypted ports will be selected automatically when SSL is enabled and
no explicit port is specified. The --sslproto option can be used to
select the SSL protocols (default: v2 or v3). The --sslcertck command
line or sslcertck run control file option should be used to force
strict certificate checking - see below.
If SSL is not configured, fetchmail will usually opportunistically try
to use TLS. TLS can be enforced by using --sslproto "TLS1". TLS connec-
tions use the same port as the unencrypted version of the protocol and
negotiate TLS via special parameter. The --sslcertck command line or
sslcertck run control file option should be used to force strict cer-
tificate checking - see below.
--sslcertck recommended: When connecting to an SSL or TLS encrypted
server, the server presents a certificate to the client for validation.
The certificate is checked to verify that the common name in the cer-
tificate matches the name of the server being contacted and that the
effective and expiration dates in the certificate indicate that it is
currently valid. If any of these checks fail, a warning message is
printed, but the connection continues. The server certificate does not
need to be signed by any specific Certifying Authority and may be a
"self-signed" certificate. If the --sslcertck command line option or
sslcertck run control file option is used, fetchmail will instead abort
if any of these checks fail. Use of the sslcertck or --sslcertck option
is advised.
Some SSL encrypted servers may request a client side certificate. A
client side public SSL certificate and private SSL key may be speci-
fied. If requested by the server, the client certificate is sent to
the server for validation. Some servers may require a valid client
certificate and may refuse connections if a certificate is not provided
or if the certificate is not valid. Some servers may require client
side certificates be signed by a recognized Certifying Authority. The
format for the key files and the certificate files is that required by
the underlying SSL libraries (OpenSSL in the general case).
A word of care about the use of SSL: While above mentioned setup with
self-signed server certificates retrieved over the wires can protect
you from a passive eavesdropper, it doesn't help against an active
attacker. It's clearly an improvement over sending the passwords in
clear, but you should be aware that a man-in-the-middle attack is triv-
ially possible (in particular with tools such as dsniff, http://mon-
key.org/~dugsong/dsniff/). Use of strict certificate checking with a
certification authority recognized by server and client, or perhaps of
an SSH tunnel (see below for some examples) is preferable if you care
seriously about the security of your mailbox and passwords.
ESMTP AUTH
fetchmail also supports authentication to the ESMTP server on the
client side according to RFC 2554. You can specify a name/password
pair to be used with the keywords 'esmtpname' and 'esmtppassword'; the
former defaults to the username of the calling user.
DAEMON MODE
Introducing the daemon mode
In daemon mode, fetchmail puts itself into the background and runs for-
ever, querying each specified host and then sleeping for a given
polling interval.
Starting the daemon mode
There are several ways to make fetchmail work in daemon mode. On the
command line, --daemon <interval> or -d <interval> option runs fetch-
mail in daemon mode. You must specify a numeric argument which is a
polling interval (time to wait after completing a whole poll cycle with
the last server and before starting the next poll cycle with the first
server) in seconds.
Example: simply invoking
fetchmail -d 900
will, therefore, poll all the hosts described in your ~/.fetchmailrc
file (except those explicitly excluded with the 'skip' verb) a bit less
often than once every 15 minutes (exactly: 15 minutes + time that the
poll take)
It is also possible to set a polling interval in your ~/.fetchmailrc
file by saying 'set daemon <interval>', where <interval> is an integer
number of seconds. If you do this, fetchmail will always start in dae-
mon mode unless you override it with the command-line option --daemon 0
or -d0.
Only one daemon process is permitted per user; in daemon mode, fetch-
mail sets up a per-user lockfile to guarantee this. (You can however
cheat and set the FETCHMAILHOME environment variable to overcome this
setting, but in that case, it is your responsibility to make sure you
aren't polling the same server with two processes at the same time.)
Awakening the background daemon
Normally, calling fetchmail with a daemon in the background sends a
wake-up signal to the daemon and quits without output. The background
daemon then starts its next poll cycle immediately. The wake-up sig-
nal, SIGUSR1, can also be sent manually. The wake-up action also clears
any 'wedged' flags indicating that connections have wedged due to
failed authentication or multiple timeouts.
Terminating the background daemon
The option --quit will kill a running daemon process instead of waking
it up (if there is no such process, fetchmail will notify you). If the
--quit option appears last on the command line, fetchmail will kill the
running daemon process and then quit. Otherwise, fetchmail will first
kill a running daemon process and then continue running with the other
options.
Useful options for daemon mode
The -L <filename> or --logfile <filename> option (keyword: set logfile)
is only effective when fetchmail is detached and in daemon mode. Note
that the logfile must exist BEFORE fetchmail is run, you can use the
touch(1) command with the filename as its sole argument to create it.
This option allows you to redirect status messages into a specified
logfile (follow the option with the logfile name). The logfile is
opened for append, so previous messages aren't deleted. This is pri-
marily useful for debugging configurations. Note that fetchmail does
not detect if the logfile is rotated, the logfile is only opened once
when fetchmail starts. You need to restart fetchmail after rotating the
logfile and before compressing it (if applicable).
The --syslog option (keyword: set syslog) allows you to redirect status
and error messages emitted to the syslog(3) system daemon if available.
Messages are logged with an id of fetchmail, the facility LOG_MAIL, and
priorities LOG_ERR, LOG_ALERT or LOG_INFO. This option is intended for
logging status and error messages which indicate the status of the dae-
mon and the results while fetching mail from the server(s). Error mes-
sages for command line options and parsing the .fetchmailrc file are
still written to stderr, or to the specified log file. The --nosyslog
option turns off use of syslog(3), assuming it's turned on in the
~/.fetchmailrc file, or that the -L or --logfile <file> option was
used.
The -N or --nodetach option suppresses backgrounding and detachment of
the daemon process from its control terminal. This is useful for
debugging or when fetchmail runs as the child of a supervisor process
such as init(8) or Gerrit Pape's runit. Note that this also causes the
logfile option to be ignored (though perhaps it shouldn't).
Note that while running in daemon mode polling a POP2 or IMAP2bis
server, transient errors (such as DNS failures or sendmail delivery
refusals) may force the fetchall option on for the duration of the next
polling cycle. This is a robustness feature. It means that if a mes-
sage is fetched (and thus marked seen by the mailserver) but not deliv-
ered locally due to some transient error, it will be re-fetched during
the next poll cycle. (The IMAP logic doesn't delete messages until
they're delivered, so this problem does not arise.)
If you touch or change the ~/.fetchmailrc file while fetchmail is run-
ning in daemon mode, this will be detected at the beginning of the next
poll cycle. When a changed ~/.fetchmailrc is detected, fetchmail
rereads it and restarts from scratch (using exec(2); no state informa-
tion is retained in the new instance). Note also that if you break the
~/.fetchmailrc file's syntax, the new instance will softly and silently
vanish away on startup.
ADMINISTRATIVE OPTIONS
The --postmaster <name> option (keyword: set postmaster) specifies the
last-resort username to which multidrop mail is to be forwarded if no
matching local recipient can be found. It is also used as destination
of undeliverable mail if the 'bouncemail' global option is off and
additionally for spam-blocked mail if the 'bouncemail' global option is
off and the 'spambounce' global option is on. This option defaults to
the user who invoked fetchmail. If the invoking user is root, then the
default of this option is the user 'postmaster'. Setting postmaster to
the empty string causes such mail as described above to be discarded -
this however is usually a bad idea. See also the description of the
'FETCHMAILUSER' environment variable in the ENVIRONMENT section below.
The --nobounce behaves like the "set no bouncemail" global option,
which see.
The --invisible option (keyword: set invisible) tries to make fetchmail
invisible. Normally, fetchmail behaves like any other MTA would -- it
generates a Received header into each message describing its place in
the chain of transmission, and tells the MTA it forwards to that the
mail came from the machine fetchmail itself is running on. If the
invisible option is on, the Received header is suppressed and fetchmail
tries to spoof the MTA it forwards to into thinking it came directly
from the mailserver host.
The --showdots option (keyword: set showdots) forces fetchmail to show
progress dots even if the current tty is not stdout (for example log-
files). Fetchmail shows the dots by default when run in nodetach mode
or when daemon mode is not enabled.
By specifying the --tracepolls option, you can ask fetchmail to add
information to the Received header on the form "polling {label} account
{user}", where {label} is the account label (from the specified rcfile,
normally ~/.fetchmailrc) and {user} is the username which is used to
log on to the mail server. This header can be used to make filtering
email where no useful header information is available and you want mail
from different accounts sorted into different mailboxes (this could,
for example, occur if you have an account on the same server running a
mailing list, and are subscribed to the list using that account). The
default is not adding any such header. In .fetchmailrc, this is called
'tracepolls'.
RETRIEVAL FAILURE MODES
The protocols fetchmail uses to talk to mailservers are next to bullet-
proof. In normal operation forwarding to port 25, no message is ever
deleted (or even marked for deletion) on the host until the SMTP lis-
tener on the client side has acknowledged to fetchmail that the message
has been either accepted for delivery or rejected due to a spam block.
When forwarding to an MDA, however, there is more possibility of error.
Some MDAs are 'safe' and reliably return a nonzero status on any deliv-
ery error, even one due to temporary resource limits. The maildrop(1)
program is like this; so are most programs designed as mail transport
agents, such as sendmail(1), including the sendmail wrapper of Postfix
and exim(1). These programs give back a reliable positive acknowledge-
ment and can be used with the mda option with no risk of mail loss.
Unsafe MDAs, though, may return 0 even on delivery failure. If this
happens, you will lose mail.
The normal mode of fetchmail is to try to download only 'new' messages,
leaving untouched (and undeleted) messages you have already read
directly on the server (or fetched with a previous fetchmail --keep).
But you may find that messages you've already read on the server are
being fetched (and deleted) even when you don't specify --all. There
are several reasons this can happen.
One could be that you're using POP2. The POP2 protocol includes no
representation of 'new' or 'old' state in messages, so fetchmail must
treat all messages as new all the time. But POP2 is obsolete, so this
is unlikely.
A potential POP3 problem might be servers that insert messages in the
middle of mailboxes (some VMS implementations of mail are rumored to do
this). The fetchmail code assumes that new messages are appended to
the end of the mailbox; when this is not true it may treat some old
messages as new and vice versa. Using UIDL whilst setting fastuidl 0
might fix this, otherwise, consider switching to IMAP.
Yet another POP3 problem is that if they can't make tempfiles in the
user's home directory, some POP3 servers will hand back an undocumented
response that causes fetchmail to spuriously report "No mail".
The IMAP code uses the presence or absence of the server flag \Seen to
decide whether or not a message is new. This isn't the right thing to
do, fetchmail should check the UIDVALIDITY and use UID, but it doesn't
do that yet. Under Unix, it counts on your IMAP server to notice the
BSD-style Status flags set by mail user agents and set the \Seen flag
from them when appropriate. All Unix IMAP servers we know of do this,
though it's not specified by the IMAP RFCs. If you ever trip over a
server that doesn't, the symptom will be that messages you have already
read on your host will look new to the server. In this (unlikely)
case, only messages you fetched with fetchmail --keep will be both
undeleted and marked old.
In ETRN and ODMR modes, fetchmail does not actually retrieve messages;
instead, it asks the server's SMTP listener to start a queue flush to
the client via SMTP. Therefore it sends only undelivered messages.
SPAM FILTERING
Many SMTP listeners allow administrators to set up 'spam filters' that
block unsolicited email from specified domains. A MAIL FROM or DATA
line that triggers this feature will elicit an SMTP response which
(unfortunately) varies according to the listener.
Newer versions of sendmail return an error code of 571.
According to RFC2821, the correct thing to return in this situation is
550 "Requested action not taken: mailbox unavailable" (the draft adds
"[E.g., mailbox not found, no access, or command rejected for policy
reasons].").
Older versions of the exim MTA return 501 "Syntax error in parameters
or arguments".
The postfix MTA runs 554 as an antispam response.
Zmailer may reject code with a 500 response (followed by an enhanced
status code that contains more information).
Return codes which fetchmail treats as antispam responses and discards
the message can be set with the 'antispam' option. This is one of the
only three circumstance under which fetchmail ever discards mail (the
others are the 552 and 553 errors described below, and the suppression
of multidropped messages with a message-ID already seen).
If fetchmail is fetching from an IMAP server, the antispam response
will be detected and the message rejected immediately after the headers
have been fetched, without reading the message body. Thus, you won't
pay for downloading spam message bodies.
By default, the list of antispam responses is empty.
If the spambounce global option is on, mail that is spam-blocked trig-
gers an RFC1892/RFC1894 bounce message informing the originator that we
do not accept mail from it. See also BUGS.
SMTP/ESMTP ERROR HANDLING
Besides the spam-blocking described above, fetchmail takes special
actions on the following SMTP/ESMTP error responses
452 (insufficient system storage)
Leave the message in the server mailbox for later retrieval.
552 (message exceeds fixed maximum message size)
Delete the message from the server. Send bounce-mail to the orig-
inator.
553 (invalid sending domain)
Delete the message from the server. Don't even try to send
bounce-mail to the originator.
Other errors trigger bounce mail back to the originator. See also BUGS.
THE RUN CONTROL FILE
The preferred way to set up fetchmail is to write a .fetchmailrc file
in your home directory (you may do this directly, with a text editor,
or indirectly via fetchmailconf). When there is a conflict between the
command-line arguments and the arguments in this file, the command-line
arguments take precedence.
To protect the security of your passwords, your ~/.fetchmailrc may not
normally have more than 0700 (u=rwx,g=,o=) permissions; fetchmail will
complain and exit otherwise (this check is suppressed when --version is
on).
You may read the .fetchmailrc file as a list of commands to be executed
when fetchmail is called with no arguments.
Run Control Syntax
Comments begin with a '#' and extend through the end of the line. Oth-
erwise the file consists of a series of server entries or global option
statements in a free-format, token-oriented syntax.
There are four kinds of tokens: grammar keywords, numbers (i.e. decimal
digit sequences), unquoted strings, and quoted strings. A quoted
string is bounded by double quotes and may contain whitespace (and
quoted digits are treated as a string). Note that quoted strings will
also contain line feed characters if they run across two or more lines,
unless you use a backslash to join lines (see below). An unquoted
string is any whitespace-delimited token that is neither numeric,
string quoted nor contains the special characters ',', ';', ':', or
'='.
Any amount of whitespace separates tokens in server entries, but is
otherwise ignored. You may use backslash escape sequences (\n for LF,
\t for HT, \b for BS, \r for CR, \nnn for decimal (where nnn cannot
start with a 0), \0ooo for octal, and \xhh for hex) to embed non-print-
able characters or string delimiters in strings. In quoted strings, a
backslash at the very end of a line will cause the backslash itself and
the line feed (LF or NL, new line) character to be ignored, so that you
can wrap long strings. Without the backslash at the line end, the line
feed character would become part of the string.
Warning: while these resemble C-style escape sequences, they are not
the same. fetchmail only supports these eight styles. C supports more
escape sequences that consist of backslash (\) and a single character,
but does not support decimal codes and does not require the leading 0
in octal notation. Example: fetchmail interprets \233 the same as \xE9
(Latin small letter e with acute), where C would interpret \233 as
octal 0233 = \x9B (CSI, control sequence introducer).
Each server entry consists of one of the keywords 'poll' or 'skip',
followed by a server name, followed by server options, followed by any
number of user (or username) descriptions, followed by user options.
Note: the most common cause of syntax errors is mixing up user and
server options or putting user options before the user descriptions.
For backward compatibility, the word 'server' is a synonym for 'poll'.
You can use the noise keywords 'and', 'with', 'has', 'wants', and
'options' anywhere in an entry to make it resemble English. They're
ignored, but but can make entries much easier to read at a glance. The
punctuation characters ':', ';' and ',' are also ignored.
Poll vs. Skip
The 'poll' verb tells fetchmail to query this host when it is run with
no arguments. The 'skip' verb tells fetchmail not to poll this host
unless it is explicitly named on the command line. (The 'skip' verb
allows you to experiment with test entries safely, or easily disable
entries for hosts that are temporarily down.)
Keyword/Option Summary
Here are the legal options. Keyword suffixes enclosed in square brack-
ets are optional. Those corresponding to short command-line options
are followed by '-' and the appropriate option letter. If option is
only relevant to a single mode of operation, it is noted as 's' or 'm'
for singledrop- or multidrop-mode, respectively.
Here are the legal global options:
Keyword Opt Mode Function
--------------------------------------------------------------------
set daemon -d Set a background poll interval in
seconds.
set postmaster Give the name of the last-resort
mail recipient (default: user run-
ning fetchmail, "postmaster" if
run by the root user)
set bouncemail Direct error mail to the sender
(default)
set no bouncemail Direct error mail to the local
postmaster (as per the 'postmas-
ter' global option above).
set no spambounce Do not bounce spam-blocked mail
(default).
set spambounce Bounce blocked spam-blocked mail
(as per the 'antispam' user
option) back to the destination as
indicated by the 'bouncemail'
global option. Warning: Do not
use this to bounce spam back to
the sender - most spam is sent
with false sender address and thus
this option hurts innocent
bystanders.
set logfile -L Name of a file to append error and
status messages to.
set idfile -i Name of the file to store UID
lists in.
set syslog Do error logging through sys-
log(3).
set no syslog Turn off error logging through
syslog(3). (default)
set properties String value that is ignored by
fetchmail (may be used by exten-
sion scripts).
Here are the legal server options:
Keyword Opt Mode Function
-----------------------------------------------------------------
via Specify DNS name of mailserver,
overriding poll name
proto[col] -p Specify protocol (case insensi-
tive): POP2, POP3, IMAP, APOP,
KPOP
local[domains] m Specify domain(s) to be regarded
as local
port Specify TCP/IP service port (obso-
lete, use 'service' instead).
service -P Specify service name (a numeric
value is also allowed and consid-
ered a TCP/IP port number).
auth[enticate] Set authentication type (default
'any')
timeout -t Server inactivity timeout in sec-
onds (default 300)
envelope -E m Specify envelope-address header
name
no envelope m Disable looking for envelope
address
qvirtual -Q m Qmail virtual domain prefix to
remove from user name
aka m Specify alternate DNS names of
mailserver
interface -I specify IP interface(s) that must
be up for server poll to take
place
monitor -M Specify IP address to monitor for
activity
plugin Specify command through which to
make server connections.
plugout Specify command through which to
make listener connections.
dns m Enable DNS lookup for multidrop
(default)
no dns m Disable DNS lookup for multidrop
checkalias m Do comparison by IP address for
multidrop
no checkalias m Do comparison by name for mul-
tidrop (default)
uidl -U Force POP3 to use client-side
UIDLs (recommended)
no uidl Turn off POP3 use of client-side
UIDLs (default)
interval Only check this site every N poll
cycles; N is a numeric argument.
tracepolls Add poll tracing information to
the Received header
principal Set Kerberos principal (only use-
ful with IMAP and kerberos)
esmtpname Set name for RFC2554 authentica-
tion to the ESMTP server.
esmtppassword Set password for RFC2554 authenti-
cation to the ESMTP server.
Here are the legal user descriptions and options:
Keyword Opt Mode Function
-------------------------------------------------------------------
user[name] -u This is the user description and
must come first after server
description and after possible
server options, and before user
options.
It sets the remote user name if by
itself or followed by 'there', or
the local user name if followed by
'here'.
is Connect local and remote user
names
to Connect local and remote user
names
pass[word] Specify remote account password
ssl Connect to server over the speci-
fied base protocol using SSL
encryption
sslcert Specify file for client side pub-
lic SSL certificate
sslkey Specify file for client side pri-
vate SSL key
sslproto Force ssl protocol for connection
folder -r Specify remote folder to query
smtphost -S Specify smtp host(s) to forward to
fetchdomains m Specify domains for which mail
should be fetched
smtpaddress -D Specify the domain to be put in
RCPT TO lines
smtpname Specify the user and domain to be
put in RCPT TO lines
antispam -Z Specify what SMTP returns are
interpreted as spam-policy blocks
mda -m Specify MDA for local delivery
bsmtp -o Specify BSMTP batch file to append
to
preconnect Command to be executed before each
connection
postconnect Command to be executed after each
connection
keep -k Don't delete seen messages from
server (for POP3, uidl is recom-
mended)
flush -F Flush all seen messages before
querying (DANGEROUS)
limitflush Flush all oversized messages
before querying
fetchall -a Fetch all messages whether seen or
not
rewrite Rewrite destination addresses for
reply (default)
stripcr Strip carriage returns from ends
of lines
forcecr Force carriage returns at ends of
lines
pass8bits Force BODY=8BITMIME to ESMTP lis-
tener
dropstatus Strip Status and X-Mozilla-Status
lines out of incoming mail
dropdelivered Strip Delivered-To lines out of
incoming mail
mimedecode Convert quoted-printable to 8-bit
in MIME messages
idle Idle waiting for new messages
after each poll (IMAP only)
no keep -K Delete seen messages from server
(default)
no flush Don't flush all seen messages
before querying (default)
no fetchall Retrieve only new messages
(default)
no rewrite Don't rewrite headers
no stripcr Don't strip carriage returns
(default)
no forcecr Don't force carriage returns at
EOL (default)
no pass8bits Don't force BODY=8BITMIME to ESMTP
listener (default)
no dropstatus Don't drop Status headers
(default)
no dropdelivered Don't drop Delivered-To headers
(default)
no mimedecode Don't convert quoted-printable to
8-bit in MIME messages (default)
no idle Don't idle waiting for new mes-
sages after each poll (IMAP only)
limit -l Set message size limit
warnings -w Set message size warning interval
batchlimit -b Max # messages to forward in sin-
gle connect
fetchlimit -B Max # messages to fetch in single
connect
fetchsizelimit Max # message sizes to fetch in
single transaction
fastuidl Use binary search for first unseen
message (POP3 only)
expunge -e Perform an expunge on every #th
message (IMAP and POP3 only)
properties String value is ignored by fetch-
mail (may be used by extension
scripts)
All user options must begin with a user description (user or username
option) and follow all server descriptions and options.
In the .fetchmailrc file, the 'envelope' string argument may be pre-
ceded by a whitespace-separated number. This number, if specified, is
the number of such headers to skip over (that is, an argument of 1
selects the second header of the given type). This is sometime useful
for ignoring bogus envelope headers created by an ISP's local delivery
agent or internal forwards (through mail inspection systems, for
instance).
Keywords Not Corresponding To Option Switches
The 'folder' and 'smtphost' options (unlike their command-line equiva-
lents) can take a space- or comma-separated list of names following
them.
All options correspond to the obvious command-line arguments, except
the following: 'via', 'interval', 'aka', 'is', 'to', 'dns'/'no dns',
'checkalias'/'no checkalias', 'password', 'preconnect', 'postconnect',
'localdomains', 'stripcr'/'no stripcr', 'forcecr'/'no forcecr',
'pass8bits'/'no pass8bits' 'dropstatus/no dropstatus', 'dropdeliv-
ered/no dropdelivered', 'mimedecode/no mimedecode', 'no idle', and 'no
envelope'.
The 'via' option is for if you want to have more than one configuration
pointing at the same site. If it is present, the string argument will
be taken as the actual DNS name of the mailserver host to query. This
will override the argument of poll, which can then simply be a distinct
label for the configuration (e.g. what you would give on the command
line to explicitly query this host).
The 'interval' option (which takes a numeric argument) allows you to
poll a server less frequently than the basic poll interval. If you say
'interval N' the server this option is attached to will only be queried
every N poll intervals.
Singledrop vs. Multidrop options
Please ensure you read the section titled THE USE AND ABUSE OF MUL-
TIDROP MAILBOXES if you intend to use multidrop mode.
The 'is' or 'to' keywords associate the following local (client)
name(s) (or server-name to client-name mappings separated by =) with
the mailserver user name in the entry. If an is/to list has '*' as its
last name, unrecognized names are simply passed through. Note that
until fetchmail version 6.3.4 inclusively, these lists could only con-
tain local parts of user names (fetchmail would only look at the part
before the @ sign). fetchmail versions 6.3.5 and newer support full
addresses on the left hand side of these mappings, and they take prece-
dence over any 'localdomains', 'aka', 'via' or similar mappings.
A single local name can be used to support redirecting your mail when
your username on the client machine is different from your name on the
mailserver. When there is only a single local name, mail is forwarded
to that local username regardless of the message's Received, To, Cc,
and Bcc headers. In this case, fetchmail never does DNS lookups.
When there is more than one local name (or name mapping), fetchmail
looks at the envelope header, if configured, and otherwise at the
Received, To, Cc, and Bcc headers of retrieved mail (this is 'multidrop
mode'). It looks for addresses with hostname parts that match your
poll name or your 'via', 'aka' or 'localdomains' options, and usually
also for hostname parts which DNS tells it are aliases of the
mailserver. See the discussion of 'dns', 'checkalias', 'localdomains',
and 'aka' for details on how matching addresses are handled.
If fetchmail cannot match any mailserver usernames or localdomain
addresses, the mail will be bounced. Normally it will be bounced to
the sender, but if the 'bouncemail' global option is off, the mail will
go to the local postmaster instead. (see the 'postmaster' global
option). See also BUGS.
The 'dns' option (normally on) controls the way addresses from mul-
tidrop mailboxes are checked. On, it enables logic to check each host
address that does not match an 'aka' or 'localdomains' declaration by
looking it up with DNS. When a mailserver username is recognized
attached to a matching hostname part, its local mapping is added to the
list of local recipients.
The 'checkalias' option (normally off) extends the lookups performed by
the 'dns' keyword in multidrop mode, providing a way to cope with
remote MTAs that identify themselves using their canonical name, while
they're polled using an alias. When such a server is polled, checks to
extract the envelope address fail, and fetchmail reverts to delivery
using the To/Cc/Bcc headers (See below 'Header vs. Envelope
addresses'). Specifying this option instructs fetchmail to retrieve
all the IP addresses associated with both the poll name and the name
used by the remote MTA and to do a comparison of the IP addresses.
This comes in handy in situations where the remote server undergoes
frequent canonical name changes, that would otherwise require modifica-
tions to the rcfile. 'checkalias' has no effect if 'no dns' is speci-
fied in the rcfile.
The 'aka' option is for use with multidrop mailboxes. It allows you to
pre-declare a list of DNS aliases for a server. This is an optimiza-
tion hack that allows you to trade space for speed. When fetchmail,
while processing a multidrop mailbox, grovels through message headers
looking for names of the mailserver, pre-declaring common ones can save
it from having to do DNS lookups. Note: the names you give as argu-
ments to 'aka' are matched as suffixes -- if you specify (say) 'aka
netaxs.com', this will match not just a hostname netaxs.com, but any
hostname that ends with '.netaxs.com'; such as (say) pop3.netaxs.com
and mail.netaxs.com.
The 'localdomains' option allows you to declare a list of domains which
fetchmail should consider local. When fetchmail is parsing address
lines in multidrop modes, and a trailing segment of a host name matches
a declared local domain, that address is passed through to the listener
or MDA unaltered (local-name mappings are not applied).
If you are using 'localdomains', you may also need to specify 'no enve-
lope', which disables fetchmail's normal attempt to deduce an envelope
address from the Received line or X-Envelope-To header or whatever
header has been previously set by 'envelope'. If you set 'no envelope'
in the defaults entry it is possible to undo that in individual entries
by using 'envelope <string>'. As a special case, 'envelope "Received"'
restores the default parsing of Received lines.
The password option requires a string argument, which is the password
to be used with the entry's server.
The 'preconnect' keyword allows you to specify a shell command to be
executed just before each time fetchmail establishes a mailserver con-
nection. This may be useful if you are attempting to set up secure POP
connections with the aid of ssh(1). If the command returns a nonzero
status, the poll of that mailserver will be aborted.
Similarly, the 'postconnect' keyword similarly allows you to specify a
shell command to be executed just after each time a mailserver connec-
tion is taken down.
The 'forcecr' option controls whether lines terminated by LF only are
given CRLF termination before forwarding. Strictly speaking RFC821
requires this, but few MTAs enforce the requirement it so this option
is normally off (only one such MTA, qmail, is in significant use at
time of writing).
The 'stripcr' option controls whether carriage returns are stripped out
of retrieved mail before it is forwarded. It is normally not necessary
to set this, because it defaults to 'on' (CR stripping enabled) when
there is an MDA declared but 'off' (CR stripping disabled) when for-
warding is via SMTP. If 'stripcr' and 'forcecr' are both on, 'stripcr'
will override.
The 'pass8bits' option exists to cope with Microsoft mail programs that
stupidly slap a "Content-Transfer-Encoding: 7bit" on everything. With
this option off (the default) and such a header present, fetchmail
declares BODY=7BIT to an ESMTP-capable listener; this causes problems
for messages actually using 8-bit ISO or KOI-8 character sets, which
will be garbled by having the high bits of all characters stripped. If
'pass8bits' is on, fetchmail is forced to declare BODY=8BITMIME to any
ESMTP-capable listener. If the listener is 8-bit-clean (as all the
major ones now are) the right thing will probably result.
The 'dropstatus' option controls whether nonempty Status and X-Mozilla-
Status lines are retained in fetched mail (the default) or discarded.
Retaining them allows your MUA to see what messages (if any) were
marked seen on the server. On the other hand, it can confuse some new-
mail notifiers, which assume that anything with a Status line in it has
been seen. (Note: the empty Status lines inserted by some buggy POP
servers are unconditionally discarded.)
The 'dropdelivered' option controls whether Delivered-To headers will
be kept in fetched mail (the default) or discarded. These headers are
added by Qmail and Postfix mailservers in order to avoid mail loops but
may get in your way if you try to "mirror" a mailserver within the same
domain. Use with caution.
The 'mimedecode' option controls whether MIME messages using the
quoted-printable encoding are automatically converted into pure 8-bit
data. If you are delivering mail to an ESMTP-capable, 8-bit-clean lis-
tener (that includes all of the major MTAs like sendmail), then this
will automatically convert quoted-printable message headers and data
into 8-bit data, making it easier to understand when reading mail. If
your e-mail programs know how to deal with MIME messages, then this
option is not needed. The mimedecode option is off by default, because
doing RFC2047 conversion on headers throws away character-set informa-
tion and can lead to bad results if the encoding of the headers differs
from the body encoding.
The 'idle' option is intended to be used with IMAP servers supporting
the RFC2177 IDLE command extension, but does not strictly require it.
If it is enabled, and fetchmail detects that IDLE is supported, an IDLE
will be issued at the end of each poll. This will tell the IMAP server
to hold the connection open and notify the client when new mail is
available. If IDLE is not supported, fetchmail will simulate it by
periodically issuing NOOP. If you need to poll a link frequently, IDLE
can save bandwidth by eliminating TCP/IP connects and LOGIN/LOGOUT
sequences. On the other hand, an IDLE connection will eat almost all of
your fetchmail's time, because it will never drop the connection and
allow other polls to occur unless the server times out the IDLE. It
also doesn't work with multiple folders; only the first folder will
ever be polled.
The 'properties' option is an extension mechanism. It takes a string
argument, which is ignored by fetchmail itself. The string argument
may be used to store configuration information for scripts which
require it. In particular, the output of '--configdump' option will
make properties associated with a user entry readily available to a
Python script.
Miscellaneous Run Control Options
The words 'here' and 'there' have useful English-like significance.
Normally 'user eric is esr' would mean that mail for the remote user
'eric' is to be delivered to 'esr', but you can make this clearer by
saying 'user eric there is esr here', or reverse it by saying 'user esr
here is eric there'
Legal protocol identifiers for use with the 'protocol' keyword are:
auto (or AUTO) (legacy, to be removed from future release)
pop2 (or POP2) (legacy, to be removed from future release)
pop3 (or POP3)
sdps (or SDPS)
imap (or IMAP)
apop (or APOP)
kpop (or KPOP)
Legal authentication types are 'any', 'password', 'kerberos', 'ker-
beros_v4', 'kerberos_v5' and 'gssapi', 'cram-md5', 'otp', 'msn' (only
for POP3), 'ntlm', 'ssh', 'external' (only IMAP). The 'password' type
specifies authentication by normal transmission of a password (the
password may be plain text or subject to protocol-specific encryption
as in CRAM-MD5); 'kerberos' tells fetchmail to try to get a Kerberos
ticket at the start of each query instead, and send an arbitrary string
as the password; and 'gssapi' tells fetchmail to use GSSAPI authentica-
tion. See the description of the 'auth' keyword for more.
Specifying 'kpop' sets POP3 protocol over port 1109 with Kerberos V4
authentication. These defaults may be overridden by later options.
There are some global option statements: 'set logfile' followed by a
string sets the same global specified by --logfile. A command-line
--logfile option will override this. Note that --logfile is only effec-
tive if fetchmail detaches itself from the terminal and the logfile
already exists before fetchmail is run. Also, 'set daemon' sets the
poll interval as --daemon does. This can be overridden by a command-
line --daemon option; in particular --daemon 0 can be used to force
foreground operation. The 'set postmaster' statement sets the address
to which multidrop mail defaults if there are no local matches.
Finally, 'set syslog' sends log messages to syslogd(8).
DEBUGGING FETCHMAIL
Fetchmail crashing
There are various ways in that fetchmail may "crash", i. e. stop opera-
tion suddenly and unexpectedly. A "crash" usually refers to an error
condition that the software did not handle by itself. A well-known
failure mode is the "segmentation fault" or "signal 11" or "SIGSEGV" or
just "segfault" for short. These can be caused by hardware or by soft-
ware problems. Software-induced segfaults can usually be reproduced
easily and in the same place, whereas hardware-induced segfaults can go
away if the computer is rebooted, or powered off for a few hours, and
can happen in random locations even if you use the software the same
way.
For solving hardware-induced segfaults, find the faulty component and
repair or replace it. <http://www.bitwizard.nl/sig11/> may help you
with details.
For solving software-induced segfaults, the developers may need a
"stack backtrace".
Enabling fetchmail core dumps
By default, fetchmail suppresses core dumps as these might contain
passwords and other sensitive information. For debugging fetchmail
crashes, obtaining a "stack backtrace" from a core dump is often the
quickest way to solve the problem, and when posting your problem on a
mailing list, the developers may ask you for a "backtrace".
1. To get useful backtraces, fetchmail needs to be installed without
getting stripped of its compilation symbols. Unfortunately, most
binary packages that are installed are stripped, and core files from
symbol-stripped programs are worthless. So you may need to recompile
fetchmail. On many systems, you can type
file `which fetchmail`
to find out if fetchmail was symbol-stripped or not. If yours was
unstripped, fine, proceed, if it was stripped, you need to recompile
the source code first. You do not usually need to install fetchmail in
order to debug it.
2. The shell environment that starts fetchmail needs to enable core
dumps. The key is the "maximum core (file) size" that can usually be
configured with a tool named "limit" or "ulimit". See the documentation
for your shell for details. In the popular bash shell, "ulimit -Sc
unlimited" will allow the core dump.
3. You need to tell fetchmail, too, to allow core dumps. To do this,
run fetchmail with the -d0 -v options. It is often easier to also add
--nosyslog -N as well.
Finally, you need to reproduce the crash. You can just start fetchmail
from the directory where you compiled it by typing ./fetchmail, so the
complete command line will start with ./fetchmail -Nvd0 --nosyslog and
perhaps list your other options.
After the crash, run your debugger to obtain the core dump. The debug-
ger will often be GNU GDB, you can then type (adjus