421 Excessive failed authentication

I see hundreds of posts in this forum about this subject dating all the way back to 2013.  I see no answers.  I have been struggling with this problem off and on for several years and now I can't send emails from Outlook any more.  I've used Outlook with Comcast as my server for over 20 years.  Now emails on all 3 of my computers keep getting stuck in the outbox.  The message " Task 'my email address - Sending' reported error (0x800CCC67) : '  The server responded: 421 resomta-ch2-12v.sys.comcast.net resomata ch2-12v.sys.comcast.net Excessive failed authentication, ESMTP server temporarily not available'  is displayed.

I don't want to/shouldn't have to give up OutLook.  The techs I talk to on the phone have been less than helpful.  Has anyone gotten any answers to this problem?