[Dovecot] Gotchas in switching from one server to another without impacting users?

[Timo Sirainen]

On Aug 14, 2009, at 12:36 AM, Gary Chodos wrote:

> We have to replace one mail store (foo.example.org) with another
> (bar.example.org).  I rsync'd the maildirs from foo to bar today and
> the plan is to hold all delivery (in the SMTP server) on foo over the
> weekend, rsync again (this time it should be much faster since the
> large xfer already occurred today), then flush the SMTP queue on foo
> towards bar, direct all new deliveries to bar.example.org.  Users
> currently access their IMAP mailboxes via imap.example.org.  I plan to
> just 'flip the switch' at DNS so imap.example.org points to
> bar.example.org (instead of foo.example.org) so users don't have to
> change anything on their end and should not even notice this change.

And I guess you also thought about the DNS cache TTLs?

> Is there anything else I should think about to mitigate users noticing
> a change?

If the maildirs are identical and no mails get lost during the move,  
that should be it.

>  Does the fact that the mail filenames include
> 'foo.example.org' in the file name (while new deliveries to
> bar.example.org will include that new hostname) spell trouble later on
> or can I ignore it?

Filenames don't matter.

> And finally, dovecot on foo.example.org is 1.1.7 while the new server
> is running 1.1.16.  I don't think that should be an issue, but
> mentioning it just in case.

Whenever upgrading it's a good idea to go through the items marked  
with "*" in NEWS file (http://dovecot.org/doc/NEWS-1.1) There aren't  
many usually.