It likely means the mail server you're connecting to doesn't understand authentication - you can't pass username and password to it...
+++ Rick ---
From: | Rick Strahl |
To: | Dmitry Litvak |
+++ Rick ---
500 5.5.1 Command unrecognized: "auth login"
What does it mean?
Thank you in advance.
It appears that the message meant that something was wrong with authentication. I changed the email server IP and the error went away.