Been working this one for a while now, and need some help. I get the following NDR exchange on 6/18/2007 2:44 PM There was a SMTP communication problem with the recipient's email server. Please contact your system administrator. <dc2.nt-mcse.com #5.5.0 smtp;556 null byte in data> Exchange 2003, mail flows in and out w/ out issue Exchange 2007, created outbound send connector, mail flows out w/ out issue I have 2 routing group connectors : Name SourceRoutingGroup TargetRoutingGroup---- ------------------ ------------------EXCHANGE-DC2 Exchange Routing Group ... First Routing GroupDC2-EXCHANGE First Routing Group Exchange Routing Group ... All suggestions are much appreciated: Thanks, Mike

can you do a get-routinggroupconnector in powershell and post the results?

can you do a get-routinggroupconnector in powershell and post the results? also, did you create the 2003 to 2007 RG with powershell or 2003 management? If with 2003 management, delete it and recreate it with powershell.