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Recipe 8.17 Receiving Mail Without a Visible Server
8.17.1 Problem
You want to receive Internet email
without running a publicly accessible mail server or daemon.
8.17.2 Solution
Don't run a mail daemon.
Queue your mail on another ISP and use
fetchmail
to download it. Authenticate to the ISP via
SSH, and
transfer the email messages over an SSH tunnel. Then have
fetchmail invoke your local mail delivery agent
directly to deliver the mail.
~/.fetchmailrc:
poll imap.example.com with proto IMAP:
preauth ssh
plugin "ssh %h /usr/sbin/imapd";
user 'shawn' there is smith here;
mda "/usr/sbin/sendmail -oem -f %F %T"
fetchall;
no keep;
~/.bash_profile:
if [ -z "$SSH_AGENT_PID" ]
then
eval `/usr/bin/ssh-agent` > /dev/null 2> /dev/null
fi
~/.bashrc:
(/usr/bin/ssh-add -l | /bin/grep -q 'no identities') && /usr/bin/ssh-add && /usr/bin/fetchmail -d 600
8.17.3 Discussion
fetchmail is the Swiss army knife of mail
delivery. Using a powerful configuration mechanism
(~/.fetchmailrc), fetchmail
can poll remote IMAP and POP servers, retrieve messages, and forward
them through sendmail and other mail delivery
systems.For security reasons, you might not want a
sendmail
daemon visible to
the outside world, and yet you want mail delivered locally. For
example, the machine where you read mail could be behind a firewall.This recipe is run by user smith on the local machine. When he logs
in, the given commands in his .bash_profile and
.bashrc make sure an SSH agent [Recipe 6.9] is running and is loaded with the necessary
keys. Also fetchmail is launched, polling a remote
IMAP server, imap.example.com , every 10 minutes (600
seconds).
fetchmail
authenticates via SSH as user shawn@imap.example.com
and downloads all messages (fetchall) in
shawn's mailbox. These messages are delivered to
smith's local mailbox by invoking
sendmail directly (mda). Our
recipe also deletes the messages from the IMAP server (no
keep) but this is optional: you might skip this until
you're sure things are working correctly.While smith is not logged in, fetchmail
doesn't run. Mail will arrive normally on
imap.example.com , awaiting
retrieval.If you prefer to run a mail daemon (sendmail -bd)
on the machine receiving your email messages, simply delete the
mda line.fetchmail is tremendously useful and has tons of
options. The manpage is well worth reading in full.
8.17.4 See Also
fetchmail(1).
