Mail was opened & used, trash was emptied in all accounts. Went to shut down mail and Mail would not allow this to happen. The 'quit' was grey. The icon would not respond. Go to shut down the computer and Mail will not allow that either. Only a 10 sec hold on power button would allow the computer to shut down. On start up the Mail works properly but reacts as described when the trash is emptied.
First, when an application won't quit, it's usually not necessary to force a system shutdown. Select Force Quit... from the Apple menu instead.
Back up all data if you haven’t already done so. Before proceeding, you must be sure you can restore your system to the state it’s in now.
In the Finder, select Go ▹ Go to Folder... from the menu bar, copy the text on the line below into the box that opens, and press return:
Delete the selected file. Relaunch Mail. It should re-index your mailboxes. Then rebuild the mailboxes (Mailbox > Rebuild.)
Thanks, that seemes to have worked.
By the way Force Quit would not work either, it was grey indicating unuseable.
The Envelope Index would not Delete but responded to Send to Trash where it resides now until I empty the trash.
Everything seems to be back in order now.
I did not have to go to Mailbox-Rebuild, the system did it automatically for me.