"An error occurred while sending mail: The mail server sent an incorrect greeting:  resomta-ch2-13v.sys.comcast.net resomta-ch2-13v.sys.comcast.net Excessive failed authentication, ESMTP server temporarily not available."

TB has worked well for the last 10 years, but sometime in Nov or Dec we can't send emails through Comcast. They say it is a Thunderbird problem because the ports and security are configured right according to them. Lately it will work okay in the morning but not in the afternoon or evening. Today it won't send at all. I get a message as follows: "An error occurred while sending mail: The mail server sent an incorrect greeting: resomta-ch2-13v.sys.comcast.net resomta-ch2-13v.sys.comcast.net Excessive failed authentication, ESMTP server temporarily not available." Why does it work sometimes and then not at all? I have had to revert to a gmail address or send comcast emails using the web. Wading through the mechanical twit that answers the phone at Comcast and then explaining repeatedly on every call to the agent is getting old, and I don't have the 2 to 3 hours it takes to converse with them. If the call gets escalated, it results in a determination that they will have to call me back, and they never do. Then, when I call again they say the case has been closed. Anybody experience this nonsense? What can be done to get the outgoing mail to work again?