What format does Apple Mail store its emails in?

Question

We're trying to convert a user's email mailbox from Apple Mail to Outlook 2010.

We copied the files off the mac, and they are mostly directories that end in .mbox and contain a folder called Messages containing .emlx files.

The .mbox extension on the folders initially made me think that these messages were in the mbox format, but after some research I found that the mbox format is actually a single file, so that rules out it being in that format.

Answer 1

You can find a description of the format based on an reengineering effort here:

It has three parts:

1. The length of part 2, in bytes
2. The message itself
3. Message metadata (XML Property List)

Answer 2

There was a question on Stack Overflow where the answer linked to a program to convert to mbox format.

It appears to be proprietary and therefore not well documented in the public domain.