This just started last night when I got an email from auctionsniper.com which is a known sender.  When I tried to open the email, I got a message that a certificate was required from this site, however, it wouldn't allow me to check the certificate, exit the Live Mail program or open any other emails.  The only way to get out of Live Mail was to shut-down my computer and not click on that email or the one in front of it.  Through the Microsoft Community I was able to verify that the certificate for auctionsniper.com is valid until some time in 2018.

Can anyone offer help in non-technical language?