You are unable to send SMTP traffic to certain domains, and see the following error in the Message Audit Log (MAL) for Symantec Messaging Gateway (SMG):

"554 Your access to this mail system has been rejected due to the sending MTA's poor reputation"

Your domain's sending IP address may be on a domain block list (DNSBL). 

Domain blacklisting may occur when:

• Your sending IP is an open mail relay.  An open relay can allow spammers the ability to use the domain to send spam to other domains.  
• There is a mass mailing worm in your environment which is sending out large amounts of e-mail traffic.

To investigate if your domain is on Symantec's Reputation List, you can check your IP on the IP Reputation Investigation page. If the IP is on the list, you may request an investigation of the IP by completing the form and clicking Investigate.

In addition, you may wish to do a search for other third-party reputation lists and follow their instructions for removal from such lists.