is really a royal pain in the butt. most of the conversion tools only do a partial job. mb2md seems to be the best but it does not convert the from line correctly unless you are using exim for an MTA. It also does not get the file status right so everything is written to the new maildir directory. something else that makes the process painful is when you have folders containing mailboxes. And the process is *slow* when you have 2 GB of mail (yes, I will be deleting some soon).
looks like I will be debugging and rewrapping this package real soon now..
to relate this to dovecot: this is probably not the job of the imap server but it would be real nice to be able to fit in some sort of a plug-in that could automatically do the conversion on a mailbox as it is opened.
it would make migrations trivial easy. give me the ability to use python for plug-ins and I will write such a tool.
---eric