I've used T'Bird for years. I have 6 Comcast e-mail addresses. I can receive e-mail on all of them. BUT, maybe a month ago, maybe 2, I can now only send messages on ONE, my "main" C'Cast account. The one I sign in with @ xfinity.com, to manage all E addresses/accounts. When send fails, I get a message saying: Sending of the message failed. An error occurred while sending mail. The mail server responded: Please ensure your email address and authenticating user match when sending messages. Please verify that your email address is correct in your account settings and try again. So I dig into my T-Bird account settings. Each of the 6 addresses has individual settings on the "Incoming Server". When I look at "Outgoing Server", it's ONE setting (U/N & Pass) for ALL accounts", which has always been my Main CCast account! If I change one, they all change. At Comcast, all E addresses use the same password, which is why it worked FLAWLESSLY for YEARS! Now, Comcast's server APPEARS to be looking for an INDIVIDUAL U/N & Pass for EACH address, which T-Bird appears to be NOT capable of doing. Any recommendations?? Thanks & have a great day!!!