Hello AlexGrawe,

Thanks for contacting Mozilla Support. I don't have Mavericks installed to test out this issue, but I've forwarded this thread to our capable Thunderbird Support crew. They should respond once they've taken a look and had a chance to test the issue.

Thanks for your patience.

Cheers, Patrick

Hi AlexGrawe:

Unfortunately this looks like a long standing Thunderbird bug:

https://bugzilla.mozilla.org/show_bug.cgi?id=688166

There's a manual workaround here that although tedious should work:

https://bugzilla.mozilla.org/show_bug.cgi?id=688166#c12

This happens in Mac OS 10.8 also. Since I can't import my existing mailboxes into Thunderbird, Thunderbird is useless to me I'm afraid. It's a real deal-breaker :(

I have Mac OS 10.9.2 nows and the problem still exists. I have so many folders that the workaround really makes no sense. Can nobody fix this bug? I would really like to use Thunderbird instead of Mail, like a lot of people probably. But as EricRFMA wrote "It's a real deal-breaker"!

What about exporting the mail from mail as MBOX files and importing those to Thunderbird using the import export tools? https://addons.mozilla.org/en-US/thunderbird/addon/importexporttools/ Or have apple closed the MBOX door by using a not quite mbox format?

I don't use a Mac and never had, so this is vaporware.