This is one of those little "perfect gem" tools. I had five years of email in Thunderbird to move to Mac Mail, and Mac Mail simply could not get the import right (missed all sorts of mail messages) plus it took forever to attempt the import.

Eudora Mailbox Cleaner imported the whole lot in about 5 minutes, with no fuss or bother.

I had one problem during the import which turned out to be some badly formatted Thunderbird mbox files (legacy from an earlier mail app). I emailed the developer and he kindly sent me an updated beta that fixed the problem -- all in less than 4 hours!!!

Highly recommended!