Well that's definitely not the correct certificate. ALTHOUGH I did uninstall Norton and install AVG myself. I got similar to yourself in terms of the certificate BUT in my case the connection to imap.virginmedia.com on port 993 still worked with no issues.
Whatever is going on, it's not an issue with the certificate itself..
I've seen one possible fix for this issue mentioned BUT:
1. It wouldn't be an option on Virgin Media's system.
2. You shouldn't need to do it anyway.
Based on the error message the client doesn't seem to be using the SAN list correctly and only authenticating using the CN (Common Name) on the certificate however this is just supposition on my part.
I've tested this server with Outlook 365, sTunnel, and OpenSSL's s_client tool and for me it's working on each.
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