upgrading 10.04 based mail server

[Kristian Rink]

Folks;

I'm again looking into finally upgrading our Ubuntu 10.04 based e-mail
server. Tried this several times in the past and (repeatedly) failed;
that's why I gave up on it yet in the end we need to get away from
10.04 at some point. 

Here's my setup: The VM includes cyrus imapd, postfix, a local mysql
database hosting virtual aliases all along with postfix-mysql and local
user accounts. Obviously, this system is critical for our business,
transports > 5k messages per day and has a spool of roughly 500g of
mail in shared IMAP boxes, as well as a modestly complex set of cyrus
ACLs controlling access to the IMAP boxes. Completely setting this
beast up all anew is tough and risky and as it generally works, I just
wanted to do a step-by-step dist-upgrade of the base system to the most
recent version.

Unfortunately, this doesn't really work well due to a couple of changes
especially in cyrus-imapd. Has anyone successfully dist-upgraded such a
setup and can share some hints, tips, ideas with me on how to get it
done well?

TIA and all the best,
Kristian