Transition from one server to another.

[Jiri Bourek]

>
>   I have an idea how such a transition could go:
>
>   1. Upgrade the old dovecot 1.2.15 to 2.1.whateveritis from debian
>      squeeze backports.

Backports version is a bit outdated so you might want to consider using 
version from jessie, which seems to follow the upstream more closely.

The tradeoff is of course the need to pull some system libraries with it 
as well, namely libc. Newer version may interfere with whatever else you 
run on the server and you'll probably need to solve some dependencies 
manually.

It's working for me on pure dovecot server, YMMV

Other than that I more or less aggree with the post from Terry Barnum - 
stop postfix to prevent delivery of new mail, block the old IMAP/POP3 
server from regular users, use some sort of IMAP sync (either imapsync 
or - IMO - even better doveadm sync) to download data from the old 
server to the new one. After that's done, switch IP addresses and enable 
services on new server.

It'll need some late-evening/night time work and maybe console access if 
the IP switch goes wrong, but otherwise it should be hassle-free - 
particulary no need to change ppl's mail client settings this way