Exim Configuration – Listen on Port 25 for Localhost Only

eximlinux

I want to use Exim4 as an MTA for my server, but basically only to send emails. For security issues, I would like to restrict incoming connections to localhost only (I think). So there is this option in the exim4 configuration where you can specify:

IP-addresses to listen on for incomming SMTP connections:

If I put localhost there, I can perfectly well send emails via mutt and mail, but other services on my machine cannot connect to the exim daemon to send emails, especially because there is no binding to the port tcp/25 if I specify localhost in the field above.

Of course if I leave the field blank, everything works fine, but I don't want to listen for tcp/25 for anybody else than my own machine… Here is my log when all connections are accepted, for local services like ossec:

2013-10-08 12:26:13 1VTcv7-XXXXX-XX <= ossecm@myserver.edu H=localhost (notify.ossec.net) [127.0.0.1] P=smtp S=979

Best Answer

If you literally put "localhost" in that setting, try putting instead:

dc_local_interfaces='127.0.0.1 ; ::1'

During dpkg-reconfigure exim4-config, if you select *Internet site" for the type, the second question looks like this:

Please enter a semicolon-separated list of IP addresses. The Exim SMTP listener
daemon will listen on all IP addresses listed here.

An empty value will cause Exim to listen for connections on all available network
interfaces.

If this system only receives mail directly from local services (and not from other
hosts), it is suggested to prohibit external connections to the local Exim daemon.
Such services include e-mail programs (MUAs) which talk to localhost only as well
as fetchmail. External connections are impossible when 127.0.0.1 is entered here,
as this will disable listening on public network interfaces.

IP-addresses to listen on for incoming SMTP connections:

Simply put the following in that field:

127.0.0.1; ::1
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