Thunderbird cannot 'fix' problems reported by network, but if you post the complete message, someone here may have suggestions on how to proceed.

What server are you talking about ? I've seen that error message before but it was a while ago. Is it Spectrum ? What comes after the '@' in the email address? What are your current SMTP server settings for the mail acount? AS david mentions that is not a Thunderbird error message. It is an error message sent to you by the server. But, I suspect there was alot more information than just AUP#Out-1320

Sounds like an authentication issue hence the need to check smtp server settings.