Can't open new Lion Mail? - Try delete the file "Envelope index"!

Problem: can't start Mail.app after installing Lion. Mail.app repeatedIy crash when you accept the database upgrade.

Possible solution:

1. In Finder use Go to Folder... and type "~/Library/Mail".
2. Delete the index file "Envelope index".
3. Start Mail and it should work nicely.

If you fear to delete it, move it to the Desktop. Go to step 3. If Mail works, it's safe to delete the file.

This simple solution is found on many comments in this forum.