Hey there! It looks like the issue is peculiar to third-party non-Outlook originated email addresses. Only my work email was affected; gmail was not. Below is what GoDaddy through whom I obtained my domain name and email sent to me in a text in troubleshooting:
"If you were using the Windows mail app or pre-installed Classic Free Outlook for Windows, it no longer supports Professional domain-based email addresses. Microsoft is now requiring a Microsoft 365 desktop Office license to use the new Outlook apps with a Microsoft 365 Work or School account. Currently, if you have a professional email in Classic Outlook sooner or later they'll get affected. Only personal email addresses like Gmail, Yahoo, Hotmail, etc. will continue to work. To learn more, please check the article by Microsoft: https://techcommunity.microsoft.com/t5/outlook-blog/how-licensing-works-for-work-and-school-accounts-in-the-new/ba-p/4047361"
As a consequence of the above, I had to upgrade my service with GoDaddy as recommended in the quoted language above. Bummer, but it appears to have fixed the issue. Hope that this helps others having the same issue.
Best