Perhaps you might consider sharing what the error is! We know exactly what you tell us. At this point we know you have an error.

I had to install IMAP instead of POP to the email to get outgoing mail working. Works fine now. Thanks for your assistance.

Just an FYI. IMAP and POP are incoming mail protocols. Both use SMTP as an outgoing protocol.

I have no idea what happened, but changing to IMAP from POP is not it.

I had called my ISP and they told me they didn't support POP anymore. Someone the forum sent me the link and instructions to change it to IMAP and after that, my outgoing emails all send. So that WAS the solution to my problem, which only occurred after today's Thunderbird update. Thank you

I did not say it is not now working. I said changing from pop to IMAP did not do anything to fix the issue.

Adding your account again however will have created a new SMTP server entry and it might now have correct settings as you provider just gave them to you. But now you will have two outgoing servers (SMTP) so if you select the wrong one mail will not go.