http://wiki.dovecot.org/HowTo/ImapProxy
Works quite well here.
This is very interesting
Does it work ok if you want to have one machine handle the nearly all
the normal IMAP traffic, but it has the ability to proxy a few users to
a different server?
ie do you need to set it up as a proxy in front of another server, or
can you have a hybrid server?
In conjuction with some kind of imap folder sync this would be quite
cool in a multi-office setup where you can then easily move users
mailbox to the closest server where they are working and a few DNS
tricks would allow them to turn up in any office and immediately start
working.
Ed W