After sending a test message, check the Log Files for the error: (Authentication failed: cannot SASL authenticate to server ...: no mechanism available) You can fix this problem by tweaking the auth mechanisms that postfix is willing to use. First check what auth mechanism postfix is configured to use - by default, you will see:
The message could not be sent because the connection to Outgoing server (SMTP) smtp.cox.net timed out. Try again. Try again. I have spoken with my ISP (Cox Communications, Phoenix), they say my account is fine.
Sep 10, 2019 · 450 Requested action aborted (4) 450 Requested action aborted (9) 460 too many messages; 501 Connection rejected by policy (7.2) 501 Connection rejected by policy (7.7) 550 Requested action aborted (4) 550 Invalid recipient; 553 - sorry, your envelope sender is in my badmailfrom list; 553-SPF (Sender Policy Framework) domain authentication fail
Mar 01, 2020 · Possible Reason 3: If you want to send mail on behalf of another user, then ensure that the user account has required permissions (ex: SendAs or SendOnBehalf) for the account that you provided in From field.