[Dovecot] Replication -- multiple users, three or more servers?

[Timo Sirainen]

On Mon, 2013-04-22 at 11:23 -0700, Rich Wales wrote:
> I'm running Dovecot 2.2.1 on an Ubuntu 12.04.2 server, with half a dozen
> accounts for various family members.  I want to set up replication
> involving at least three Ubuntu servers, with different users replicated
> on different sets of servers.
> 
> For example, I might have mail for "user1" replicated on "server1",
> "server2", and "server3"...
> 
> while mail for "user2" would be on "server1" and "server2"...
> 
> and mail for "user3" would be on "server1" and "server3".
> 
> I've read the wiki page (http://wiki2.dovecot.org/Replication), but I'm
> still confused.  I'd love to see an example that clearly shows how to
> set up specific individual mail users to be replicated on a different
> set of servers for each user, like what I described above.

Everything is the same as in that wiki page, except you need to have
userdb field override the mail_replica setting. Or I guess you wouldn't
want to have a default mail_replica at all, so users won't accidentally
get replicated to wrong place. See
http://wiki2.dovecot.org/UserDatabase/ExtraFields

For example with SQL something like:

user_query = SELECT home, uid, gid, \
  concat('tcp:', replicahost) as mail_replica \
  FROM users WHERE userid = '%u'