"In the short term, I need one of two things: A. a way to get through to a human agent at Comcast," What worked for me was using the "Chat" feature. I went around in circles for a while getting useless repsonses from some bot until I typed "representative" which connected me with a live person (on Chat). Of course, the agent "Jason" promised me a phone call from advanced support, and that never happened. However, I haven't encountered the SMTP error for a little while, which may be coincidental.
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