We are a computer reseller in Belgium.
I can confirm the problem between Nod32 and Thunderbird 78 : disabling the SSL/TLS filtering solve the issue.
It is not the first time we have that kind of issue with Nod32 and client mails, and it is VERY bothering : since yesterday, we have received many requests for help from desperate customers.
I can't believe this problem occurs again and that questions about us keeping on proposing this product. Fortunatelly, we have an OUTSTANDING support from MGK in Luxembourg, but why we - and them - have to deal with that is beyond my understanding. Don't you try that in your labs ?
Always the same : developers are disconnected with the real world. Customers suffer.