[Dovecot] Email client dowloads previously read messages as new during migration.

I am migrating from UW to dovecot and using mbox. I have been able to find mbox to maildir migration information and tools; however, I have had little luck finding any tool or information for performing such a migration where I wish to keep mbox. ( I know I should migrate to MailDir, but in the case I wish to take baby steps.)

I have setup dovecot pop3 communication and I go to my email client and everything works fine with the exception that all mail I have previously read (when using UW as my POP server) is downloaded again as NEW. Is there a way to prevent this from happening without setting my client to delete mail from server?

thank you!