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

Question

Problem: can't start Mail.app after installing Lion. Mail.app repeatedIy crash when you accept the database upgrade.
Possible solution:
In Finder use Go to Folder... and type "~/Library/Mail".
Delete the index file "Envelope index".
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.

Answer 1

FIXED!  My case was just successfully closed with Apple and I am now able to see my mail in Lion.  It took 2 days for Apple to come up with the resolution, and I was told that there were other cases of a siimilar nature reported.
Here's what fixed it for me.  The problem had something to do with smartmailboxes, which I use in my mail.
Close the Mail app and confirm it is closed.
Open a Finder window.  Hold down the Option key while clicking Go along the top menu bar in the Finder window and click on Library.
Navigate to the mail library under your user name.  In one of the subfolders, you will find 1 or more files named smartmailboxes.plist.  There may be a file name similar to that with "backup" in the name, as well.
Drag each of those files to your desktop and ensure they are no longer in your mail library folders.
Restart Mail.  (Those .plist files will be re-built automagically.)
This fixed my problem and I was then able to delete those plist files from my desktop.  It did take a little while for the .plist files to regenerate, though.
Good luck with your fix.