Mail crashes permanently - can't open it anymore
First, try rebuilding your Mails' Envelope Index..

To do this:


log into your user
make sure Mail is NOT running.
pull down "Go", click (near the bottom item) "Go to Folder", and insert this in the window:  ~/Library/Mail/V2/MailData/
Look for:  Envelope Index
Delete it (drag to trash).. DO NOT EMPTY TRASH YET...
restart Mail.  It will tell you that it needs to rebuild the account.. this could take seconds, minutes, or hours..... do not interrupt it...


This is the fastest/best way to rebuild your Mail account...