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

[kentborg at borg.org (Kent Borg)]

Question about setting up Postfix/Dovecot machine as a backup e-mail server.

I run my own e-mail at home over a DSL connection over Verizon copper, 
which is crappy service. I currently have no dial tone, though plucky 
DSL is still working well enough for e-mail to get through. I have a 
service call into Verizon (for Saturday--they don't exactly hop into 
action, do they?), and I am worried they will break what DSL I have (it 
isn't Verizon's). They have broken my DSL in the past when I called 
about no dialtone. (This happens regularly.)

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.

I see three possibilities:

* Set up a backup that just queues messages.

     ?I don't really see the point.

* 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.

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

    Man, that starts to get complicated, tricky to get right, hard to
    test on a live system. (I have a backup domain name I could test on,
    but that doesn't make it easy.)

Suggestions? Is there a standard solution I could use that is easy and 
already debugged?

Thanks,

-kb