so did you view the certificate so you can say who issues it? Most of these posts in this forum relate to anti virus programs scanning incoming mail and offering self signed security certificate which are not build into the acceptable providers database because they are not in the chain of trust. Turning off email scanning should see the message go away.

My anti virus (avast) seems to have created this problem. I turned off email scanning, deleted the incorrect referenced exception, but still it will not allow me to read email, still putting up the popup "You are about to override how Thunderbird identifies this site.. Legitimate bankd.... and showing an old email servier which I no longer use. I have deleted the account which used that old server. Still it will not go away.

My anti virus (avast) seems to have created this problem.

Correct.

I turned off email scanning, deleted the incorrect referenced exception, but still it will not allow me to read email, still putting up the popup "You are about to override how Thunderbird identifies this site.. Legitimate bankd.... and showing an old email servier which I no longer use. I have deleted the account which used that old server. Still it will not go away.

Then perhaps go to the more troubleshooting information click on copy to clipboard and then past into a reply on the forum. Then we can look at what is being accessed.

I let iy sit there all day, came back to read your message and looked at Thunderbird and it had corrected the problem and is getting email again! I can't explain it.. but if it's fixed, then it must have just taken some time after stopping the anti-virus email program. Thanks for your help!