[Dovecot] Mixed Courier POP3 and Dovecot IMAP environment

[Ed W]

> I'm thinking about patching so the transition can be as transparent as
> possible: Also if anything might go wrong in production I want to be
> able to switch back to the 'old' Courier IMAP (without renaming files
> etc.)
>
> Any thoughts on this

I am going through the same process at the moment and I think the best 
solution is to start afresh

I have setup a new Dovecot server with the proxy stuff enabled.  I can 
then migrate accounts one at a time to the new machine and other users 
pointing at the new machine simply get proxied back to the old machine.

Can't easily roll users back to the old machine, but it does mean that 
we can do limited testing and not need to do a big bang approach

Ed W