Re: [exim] receiving mail on exim behind a :25 port firewall…

Noting that I have never had the need to use the following, the ETRN
SMTP extension specification for intermittently-connected hosts is built
in to Exim.

Look here: http://wiki.exim.org/FAQ/Dialup_and_ISDN

Essentially, mail queues on the "external" host and the "internal" hosts
calls up to it and says "ETRN domain". All mail for $domain is then
pumped down that connection.

Graeme