resomta-c2p-555953.sys.comcast.net resomta-c2p-555953.sys.comcast.net ESMTP server not available (396356/136.144.35.123)

Thanks for the follow up. I've tried 1) using my POP account from different servers in US, 2) POP account from Canada, 3) just created an IMAP account and still cannot send email without disabling the VPN. My VPN supplier is ExpressVPN, I've used them for years. I have no access to another VPN supplier at this time. The error message with IMAP is virtually the same: "resomta-c2p-555920.sys.comcast.net resomta-c2p-555920.sys.comcast.net ESMTP server not available (396356/136.144.43.96)"  I simply cannot reach the ESMTP server without disabling my VPN for the mail sends. Going to revert back to my POP account because that is where I've interacted with Comcast since the very start, decades now. This error message is new, especially the "ESMTP" - used to be simply "SMTP" but that was fixed.

A more troubling update - using the native Mail application on my MacBook Pro, I get a similar failure to using MS Outlook. Except with the Apple native mail app I can see the errors, tens upon tens of error messages, streaming back to the Mail App until apparently the connection is terminated. Something about a socket connection. If it would be helpful I can copy the final ESMTP response before terminating...  The only application that works in the native Xfinity Mail app but that app lacks flexibility afforded by other mail apps. I have followed the directions for setting up MS Outlook from both Xfinity and MS. I have my application set up as instructed, have always been setup this way. Something is amiss: either the on-line instruction for setting up a third party application are incorrect from both Xfinity and MS or... a problem exists in the implementation. This is a serious problem for me. How can this be rectified without moving to different platforms, local and otherwise? Thanks for any troubleshooting help you can provide. I've expended every option at my end...

I am sorry, but I don't have a solution for you on this inconvenient situation. The best course of action, in this case, would actually be to report this to our Customer Security Assurance to see if there is something on the back end causing this issue for you.  You can contact them by following this link: https://internetsecurity.xfinity.com/help/report-abuse/ or by calling CSA Toll-Free Number: 1-888-565-4329. -Christy