[Dovecot] preserving pop3 mail uids

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Is there some way that message uids can be preserved when converting uw-pop3 mbox mail to dovecot maildir format?
We've tried perfect_maildir, mb2md and the convert-tool that comes with dovecot but so far have been unable to preserve 
the message uids, which for example go from 44333a8500000003 before the conversion to 4434621500000003 afterwards. 
The quantity of mailboxes involved means forcing users to re-pop old emails left on the server isn't an option. Any help appreciated.