MBOX Breaker is a Mac-only program that allows you to split mailbox (.MBOX) files into smaller files of any size you desire.
Apple Mail, for instance, has a 1 GB limit on the size of .mbox files it will let you import, so MBOX Breaker could split your existing mailbox into smaller files that can be successfully imported.
Mia for Gmail (was Notifier Pro for Gmail) is a desktop Gmail client which sits politely in your menu bar.
