Overview

After sending a mailing out some members report that they did not receive the message. When you investigate the log files you discover error messages like the following and want to understand what they mean:

<-- DNS info available for: example.org
--> Attempting to connect to: example.org (xxx.xxx.xxx.xxx 25)
<-- Connected to: example.org (xxx.xxx.xxx.xxx 25)
<-- 421 4.7.0 Not allowed.
--> Mail stream 'default' is blocked by domain 'example.org' in step CONNECT.

In this error, example.org responds to ListManager with "421 4.7.0 Not allowed." and xxx.xxx.xxx.xxx 25 is the IP address and port of the server that responded when ListManager was trying to CONNECT to deliver the message.

Information

The response 421 4.7.0 Not allowed can be caused by a variety of factors, which are only known to the administrators of the domain that rejected the message. Possible reasons may include sending too high a volume of messages to the domain, the message missing some authentication item, or there is an issue with the content. The only way to resolve the issue is to contact the administrators of the domain that rejected the message and ask why. Based on their response there may be steps that you can take to resolve the issue and avoid having the domain reject your messages.