A few days ago, I began receiving the ‘Mail Shield Security Exclusion’ pop-up from Avast when attempting to access e-mail from pop.att.yahoo.com (using Thunderbird on Windows 7). It was as if the certificate had just expired but viewing the certificate showed that it actually expired 2016-12-09. I chose the option to permanently confirm security exception. How can I undo this once yahoo installs a valid certificate?
Related info: Another user describes the certificate expiration at
https://forums.yahoo.net/t5/Sending-and-receiving/EMail-site-certificate-has-expired-Avast/m-p/184480