Question: Mail opens and closes outgoing messages, without sending
Hi, today Mail stopped sending email. I compose a message, hit send, and it moves to the outbox and sits there. About every 5-10 seconds, it opens the message in a window, then closes it immediately. This continues until I finally delete the message from the outbox. It opens it one last time, then stops. I have tried the different accounts I have setup in Mail and they all behave the same. I've rebooted the Mac, with no change in symptoms. I am wondering if I need to delete all accounts and re-setup or to re-install Mail.
BTW, I can still receive email using the Mail utility.
Mail Version: 10.3 (3273)
OS Version: 10.12.6 (16G1036)
iMac (21.5-inch, Late 2013)