updating Mail archive in DTPO

I seached the forum and manual but could not find an answer so here it goes:

I have important some mailboxes from Mail into DTPO. Now what i want to do is update the imported mail in DTPO without having to redo the whole operation. How does this work?

Thanks already,

Archived emails will not be imported again unless you deleted them in the meantime from the database. You will see a log message that ‘x’ messages were previously imported.