Blacklist error message 0X800CC92

I have used Outlook on Microsoft 365 for more than a year, to access two email accounts that Xfinity has graciously grandfathered in for me. Within the past two months, my downloads to Outlook are almost invariably blocked by Comcast with a Blacklisted message and an error code of 0X800CC92. Occasionally, everything works as it should, but this has been a rarity. With one exception, I have been able to access Comcast email directly using the same passwords as in Outlook, but when I tried to create a new Outlook profile as recommended by Microsoft, it failed in roughly the same manner as the email downloading failed.

I do get email on a gmail account both directly and from one Comcast account in which I set a forwarding address. While this email uses IMAP and the two Comcast accounts are POP3, my wife has the same email problems and all of hers are IMAP, yet only the gmail seems to work regularly. Could this simply be a port problem, and if so, what are the latest advised port and security settings for POP3 and IMAP?