Google Email Uploader

Google Email Uploader for Mac is a desktop utility for Mac OS X that uploads email archives from Apple Mail, Eudora, and Thunderbird (along with other mbox and Maildir archives) to your Google Apps mailbox.
The application does not currently upload to gmail.com or googlemail.com mail accounts.
Google Email Uploader for Mac requires Mac OS X 10.4 or later, and a Google Apps mail account.