The server rejected our credentials.

Either the username, password, or challenge response given to the server was rejected.

This is considered a non-fatal error (the connection will not be dropped).

Inherited from SMTPClientError (via ESMTPClientError):

Method __init__
Method __str__ Undocumented
API Documentation for Twisted, generated by pydoctor at 2016-05-18 16:01:36.