[Discuss] Backup Postfix/Dovecot E-mail Server?

[dsr at randomstring.org (Dan Ritter)]

Kent Borg wrote: 
> Question about setting up Postfix/Dovecot machine as a backup e-mail server.
> 
> I should set up an e-mail backup. I have another static Linux machine I
> could use, that has a static IP address, but the question is how to
> configure it. Once upon a time I had a machine set up as a backup, but it
> only queued up messages until the primary machine came back on line. But
> sending machines do a decent job of queuing messages anyway, so that doesn't
> buy much, so I turned it off.

This is called a Secondary MX, although you can have any number
of them.

> I see three possibilities:
> 
> * Set up a backup that just queues messages.
> 
>     ?I don't really see the point.

It provides the illusion of high uptime, which might be
important for you. In any case, it's a set of suspenders to 
go with your belt.

> * Set up a second server that acts like the first.
> 
>     ?I worry when I might do a cutover the IMAP server will confuse the
>    client. The client won't see old messages that were on the primary
>    server and so deletes its local copies.

Yeah, that would be bad.

> * Set up something more clever that keeps the primary and backup in sync so
> both IMAP servers hold the same messages.

High-availability is hard, although this is the easiest case:
you list both machines in your MX records, and have your MTA
deliver to a shared filesystem. DRBD is the usual choice.

Then your IMAP service has to deal with all your mail in the
shared filesystem.


-dsr-