Do you have an anti virus scanning outgoing mail? That can make things incredibly slow to the point of timeouts occurring. Antivirus settings to "scan encrypted connections" can also be a significant point of failure. as encrypted connections scanning involves intercepting, decrypting, scanning, re-encrypting, and returning the data to the connection stream in basically the same way a man in the middle hack occurs. This is a very slow and CPU expensive process which is supposedly transparent but not always fast enough..

Thanks for info... I do not have email antivirus--I have Crowdstrike and they do not scan outgoing emails.. so it is a Thunderbird problem still...any additional thoughts.. I got rid of any extensions or themes as well --still not working