Rejection errors when delivering to 3rd party recipients
Last Updated September 20, 2017
An outbound email sent to a third-party recipient which resulted in a bounce back indicating that the mail delivery agent was unable to deliver your message. The list below includes some of the most common error messages the recipient mail server could return.
I was unable to deliver your message to the following addresses:
Reason: 550 5.7.1 Rejecting mail, <originating IP address> is blacklisted
Reason: 550 unknown user
Reason: 550 Denied by policy
Reason: 521 access denied
Reason: 553 Relay denied
Reason: 554 Too many Received: headers
Reason: 550 Message rejected due to sender IP reputation ([xx.xx.xx.xx])
This indicates that we attempted to deliver the message to the intended recipient’s server, but it was not accepted by that server. The solution depends on the reason provided by the recipient server. It may be an invalid address, the recipient may be blocking the mail based on content or address, or the recipient system may be misconfigured.
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