Jonathan Vanasco wrote:
> I was talking earlier with a friend about having a failover email
> system providing full redundancy
>
> Ideally something like:
>
> Mailserver A port 25 (Live)
> delivers locally to Mailserver A port 2525 maildirs
> relays a copy to Mailserver B port 2525 (backup)
>
> Mailserver B port 25 (backup)
> delivers locally to Mailserver B port 2525 maildirs
> relays a copy to Mailserver A port 2525 maildirs (live)

I have been thinking about doing something very similar to this. In my
case, I have 4 servers, each having a subset of maildirs, so A->A&B,
B->B&C, C->C&D, and D->D&A. So if A went down, D could take over its
functions if needed.

My cutover would involve taking A out of DNS and changing the database
entries for all accounts on A so Exim and Courier know where to look for
the maildir.

> my first idea was that port 25 on each machine is an exim relay station
> that just routes messages to the local mailstore and the backup mta --
> both running on port 2525.

I think what would work better is to have all your scanning happen on
the port 25 daemon (AV, SA, RBL, etc) and the 2525 daemon simply accepts
the mail (*only* from your 2 mail servers) and delivers it where is
needs to be (little or no checking).

An rsync between the servers may be able to handle changes that IMAP/POP
may have made. Just make sure if you have an outage and you switch back
to server A, that you don't let the rsync run as it normally would or
you'll lose mail.

At this point, it is all in my head. I haven't started implementing any
of it. If you do, let me know how it works out.

--
Dennis Skinner
Systems Administrator
BlueFrog Internet
http://www.bluefrog.com

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