AFAICT, Mail.app version 6.2 is found on 10.8; on Mountain Lion.
Mail.app has had some similar crashes over the years.
The following are diagnostics, and may not cure the problem.
Try rebuilding the mailbox (Mail.app > Mailbox > Rebuild) and use the connection doctor (Mail.app > Window > Connection Doctor) to test the connection.
If this is a single document that causing the issue and not multiple messages, then can you jusy delete the message?
To check tht the disk is (mostly) working and (mostly) correct, launch Disk Utility and verify and repair permissions, and repair the disk volume.
As a test, create a new user and set up mail, and see if things work in that user context. (This is aneasy way to see if there's something odd in your login.)