update thunderbird

is that on sending mail or receiving it?

Do you use anti virus that scans mail? Try disabling it in favor of defender and see if there is still an issue.

Thank you, Matt. Thunderbird frequently times out when I try to Send. I don't use an anti virus other than defender. Any other ideas? Miriam

1. The next obvious question is how large are the email you are sending? Providers allhave limits and often will just drop a connection if the request goes over that. That shows up back to you as timeout becuase Thunderbird waits for a response until the timeout period is over.
2. What mail provider are you using? They are not all created equal and some feature here far more frequently than their market penetration should allow. Yahoo features frequently along with those ISP that they provide contracted services for.
3. How fast is your internet connection? Google offers a free test. https://support.google.com/websearch/answer/6283840?visit_id=639284065693036259-2287654597&p=speedtest&rd=1