Who is the mail provider, and what are you smtp settings? The provider may have changed the requirements for authentication, such as OAuth2, secure mail key or app password.

Who is the mail provider, and what are you smtp settings? The provider may have changed the requirements for authentication, such as OAuth2, secure mail key or app password.

mail provider is go daddy, smtp settings are copied right from their set up instructions (except for port- changed to 3535) these settings worked today until I changed the password.

Which setup instructions? They have more than one, and I'm not going to guess. Post the link.

here we go

Those settings look correct, but it might make a difference if you add the geographic identifier such as smtpout.europe.secureserver.net

https://ca.godaddy.com/help/server-and-port-settings-for-workspace-email-6949

If you've changed passwords, remove the old ones from Saved Passwords in TB Options, then restart TB and enter the current, working password when prompted.

So I reached out to my provider and after trying many different settings I'm still having this same problem with my outgoing mail server. They tell me it must be a problem with the app. Any suggestions?

If it only fails with sending, check if an antivirus app is scanning outgoing mail. Many of them, such as Bitdefender, TrendMicro, Avast can cause such issues.