Comcast Email - Internet Security Warning Message Received at Outlook Startup

My current system is Windows 10 with an Outlook email configuration of two Comcast email addresses, one account is IMAP and the other is POP, and both have been defined this way for years.  Previously my Outlook version was 2019 but I upgraded to Outlook 2021 in September of 2023.  Both email accounts have been operating normally without any problems.

On the afternoon of 07/29/2024 I started to receive an “Internet Security Warning” message whenever I started Outlook.  The message dialog displayed “The target principal name is incorrect.”  The General Certificate Information indicated it was “Issued to:  imap.email.comcast.net” and had valid active certificate dates displayed.  As long as I replied “Yes” to continue using the server in the dialog box, both of my email accounts would continue to send and receive email and function completely normally.  No changes had been made to the email configuration in the past years and only Windows 10 and Microsoft Office maintenance was regularly applied.

At this point it was not clear which account or if both were involved with the security warning.  I have a new Windows 11 desktop system that I was beginning to set up as a replacement for my Windows 10 system since it could not be upgraded to Windows 11.  On this new system I also had Outlook 2021 installed and initially only configured the IMAP Comcast email address.  This account ran for a week without error but as soon as I added the second Comcast email address as a POP account the “Internet Security Warning” dialog was displayed.  Now the same problem on two different platforms and indicating it was most likely associated with the POP account.

I was in contact with Comcast email technical support over the past few days about this and also had two additional tickets opened so that I could get to successively higher-level support.  This was completely unhelpful and nothing was resolved.

Last evening (08/15/2024), I was again researching this problem and trying to figure out what was causing this.  I was back into the Outlook configuration information and happened to notice that the Incoming Server name was specified as “pop3.comcast.net.”, note the extra “.” at the end of the server name.  It was like this on both of my platforms.  On both systems I removed the extra “.” and restarted Outlook.  The “Internet Security Warning” message was no longer displayed.  I can only guess that this incorrect POP server name was preventing a successful lookup of the Comcast server names as specified in the “Details” section of the certificate, “Subject Alternative Name” list.  Since the configured server name couldn’t be found, the security warning message was being issued.

How did this configuration problem occur on both platforms?  That is still a mystery.

On my current Windows 10 platform, I can assure anyone that I was not bored on 07/29 and just decided to change the POP Incoming Server name, which initially was “mail.comcast.net”, to “pop3.comcast.net.” just for the fun of it.  Somehow at some point, it appears that a background change was automatically invoked via Outlook to update that previous server name to a new Comcast standard name.

On my new Windows 11 platform, I noticed that when Outlook 2021 was configuring each of my accounts, it was smart enough to determine from the specified email address that it was associated with Comcast email.  Then it was able to populate the basic configuration information parameters on its own for IMAP and POP accounts.  For verification, I deleted my current POP account and then redefined it.  I can see the incorrect “pop3.comcast.net.” name being automatically inserted by Outlook.

So who is really causing this?  Is Outlook directly doing this with bad info itself or is it only handling bad information that is being passed directly from Comcast?  That issue remains and resolution is a totally independent debugging problem at this point.  It certainly looks like something was recently changed to invoke this problem.