When I moved from my Windows machine to a Mac I had a bunch of mail in my Thunderbird that I wanted to migrate over. These are emails going back to the days of the war in online email services. As it turns out it isn't as easy as copying the mailboxes over from Windows to my shiny Mac. MozBackup didn't work for me because it is only for Windows-to-Windows. I found a solution after some soul searching from Google... Turns out it's almost as easy as copying over your mailboxes...1) Install the T-Bird extension MBoxInput
This is the beauty in open standard. Mailboxes in T-Bird are stored in MBox standard, therefore they are portable to whichever email client you wish to use. Install this onto your Mac T-Bird.2) Copy your mailboxes from your Windows T-Bird profile folder to your Mac
They are in your %APPDATA%\Thunderbird\Profiles folder. I used my good-ole USB drive...3) On your Mac, right click on your Folders menu, there will be a "Import/Export" item. Select it, and then choose the mailbox in your Profile folder/sub-folder you want to import (eg. Inbox)
If you have multiple email accounts set up, you can right click on the account before selecting Import/Export. The mail will then be imported into the appropriate account as a subfolder.