[Dovecot] IMAP to Maildir Migration preserving UIDs?

[Gedalya]

Hello all,

I'm facing the need to migrate from a proprietary IMAP server to 
Dovecot. The migration must be as smooth and transparent as possible.

The mailbox format I would want to use is Maildir++.

The storage format used by the current server is unknown, and I don't 
look forward to trying to reverse-engineer it. This leaves me with the 
option of reading the mailboxes using IMAP. There are tools like 
offlineimap or mbsync, and they do store the UID and UIDVALIDITY info. 
The last piece of the puzzle is a process to properly create the 
dovecot-uidlist and dovecot-uidvalidity files. So far I wasn't able to 
find anything on this. Are there any tips? Are there any tools available 
to do this job, or part of it?

In either case I need this done, and I'll have to create whatever I 
can't find available. If there isn't anything out there that I'm yet to 
become aware of, then I'm looking at creating something like an 
offlineimap post-processing routine?

Any help would be much appreciated.

Gedalya