Mail freezes with initial migration after upgrading to Mountain Lion I recently upgraded Mac os 10.5.6 to the new 10.8.1 (Mountain Lion).  So far, everything seems to work fine except Mail.app.  When I open the application for the first time, it begins migrating and then freezes. How can I solve this?
Try deleting the three files which name start with Envelope, in ~/Library/Mail/V2/MailData .