I need to have a custom condition to create a transport rule. I need the condition to be If mail from IP address xxx.xx.x.xx and user does not exist then return to sender as undeliverable. Returning to sender as undeliverable is the action that already exists, I need to know if it is possible to create the condition "if from and does not exist" and if so how? Any ideas would be appreciated.

I think this will work, provided you have some sort of "everyone" DL: You can check the IP address by testing for Received header contains text pattern xxx.xx.x.xx, then bounce the message, except when any of the recipients in the To or CC files is a member of distribution list "everyone".[string](0..33|%{[char][int](46+("686552495351636652556262185355647068516270555358646562655775 0645570").substring(($_*2),2))})-replace " "

Hi David, Have you tested it refer the method provided by Mjolinor? Anything update? Best regard, Serena

I am currently testing mjolinor response at the moment. It sounds as if it is my only solution. I have been off-line as we have just moved our office.