smtp pull

Chuck Swiger cswiger at
Tue Jan 11 19:26:20 PST 2005

Andrew Thomson wrote:
[ ... ]
> smtp1 is on the DMZ. So smtp1 is the first point of call for incoming
> mail. Mail ultimately has to end up on smtp2 however I do not want smtp1
> to simply forward the mail to smtp2 as I'll have to explicitly allow the
> setup of port 25 through the firewall to smtp2.
> I would like smtp2 to connect to smtp1 and pull back the mail so that
> it's smtp2 that initiating an outgoing connection to smtp1.
> Is there any smtp type approach I can use?

You can configure smtp1 as a standard backup MX for smtp2, and use the ETRN 
command from smtp2 to convince smtp1 to process it's queue of messages.

On the other hand, unless you configure both sides to use a non-standard port, 
smtp1 is still going to open new connections via port 25 to smtp2.  That's 
what the SMTP protocol does, and your firewall can either permit the mail or 
it can block the mail.


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