Comcast Email Security Certificate //Certificate Error Messages from Outlook for Ma

Have used Outlook for Mac (part of Office 365 for Mac) for many years as my email client program.

Recently upgraded new iMac to macOS Catalina.  All email settings have been replicated from prior successful connection with Comcast email servers.  The settings have been reviewed by Comcast tech support as well as by Microsoft tech support and nobody can find any problem wiht them.  (I can connect to other email ISP's with no problems and utilize the Web version of Comcast email with no problems.)

Condition:  Email will only download when Outlook is started.  After that time the email does not synch with Comcast IMAP incoming server, and periodically produces the following message:  "A secure connection cannot be established with the server imap.comcast.net."   I cannot download messages until I quit the program and restart it.  I have spent a few hours with Microsoft tech support and it is there conclusion that there is something amiss with Comcast communications regarding the  security certificate.

Does anyone have any ideas as to a path where I can get reasonably sophisticated tech support from Comcast to anayze and address this issue?  Anybody receiving the same certificate error message?

Thanks