Messagelabs - 501 Connection rejected by policy [7.7]

501 Connection rejected by policy [7.7] xxxxxx, please visit www.messagelabs.com/support for more details about this error message.

Customers seeing this message are probably listed in messagelabs internal RBL. Unfortunately Messagelabs will only discuss the block with their own customers. This means you need to contact the person/company you where trying to email (by phone or alternate means), and ask them to open a ticket with messagelabs by emailing support@messagelabs.com. In that support request they either need to ask Messagelabs to remove your mail servers IP address from their RBL, or ask Messagelabs to talk with you directly regarding the issue.