Blocking servers

I cannot send/receive emails since yesterday-this is what I was eventually told to do:

"Your problem is AVG. It is intercepting your secure connection to the server, and presents a cert unknown to Thunderbird. Hence Thunderbird is refusing the connection. See https://support.mozilla.org/en-US/kb/troubleshoot-SEC_ERROR_UNKNOWN_ISSUER for some general information. Unfortunately AVG isn't in the list with specific instructions. Basically you'll need to disable SSL/TLS scanning (or however it is called) in AVG. If you do need any help with this you should contact AVG support or ask in an AVG forum."

how can I fix this?

Hello Karen,

I understand the inconvenience.
Please perform repair of AVG Internet Security as mentioned in this article: http://avgread.me/1BVxDSY and enable SSL/TLS scanning.
If the issue persists do let us know.

I performed the repair and SSL/TLS is already enabled on my email program.  It's still giving the same message-anything else to try?
Thank you!

You are most welcome.

Thank you for trying repair of AVG.
In this case, we have to try reinstallation of AVG Internet Security program once.
I request you to get our additional support in performing this reinstallation and if the issue persists they can escalate to senior technical team.
An email instruction has been sent to get connected with our additional support.