When the receiving mail server is employing an antispam measure known as "Sender Address Verification," and a Symantec Brightmail Gateway (SBG) version 8.0 and above has "Connection Classification" enabled, some e-mail messages may get stuck in the Delivery Queue with the error code "450 4.7.1" and an error indicating that a recipient of those e-mail messages has been denied.
Messages are stuck in the queue with errors similar to this:
The receiving mail server is employing an antispam measure known as "Sender Address Verification". The IP address of the server attempting the verification is in a "Connection Classification" class that does not allow many simultaneous connections or messages. An SBG appliance does accept the empty address <> as required by RFCs.
To resolve this issue, do one of the two things:
Note: Most sending MTAs will fall into the "Default" classification, so it is not recommended to increase these values too much. Symantec cannot provide specific values because the default values are considered best practice. Any changes to the default values should take into consideration environmental factors such as the inbound mail volume.