Everything works with the exception of this issue: When sending an internal email from a user on the 2010 server to a user on the 2003 server it immediately ends up in the poison queue on the 2010 server. It shows this happening in the message tracking on the 2010 server, but there is no record of it in the message tracking on the 2003 server. All other functions work (internal from 2003 to 2010, internal 2003 to 2003, internal 2010 to 2010, incoming and outgoing Internet email on both). In troubleshooting I deleted the automatically created routing group connectors (using the shell) and recreated them using the shell command new-routinggroupconnector with the bidirectional switch. The 2003 server has the unmodified Default SMTP Virtual Server and an associated SMTP connector with a smart host set to the ISPs mail server. The 2010 server does not have it's own Internet send connector, but uses the 2003 server (tried both ways). The suppress link state updates reg hack has been done on the 2003 server. Both servers have been rebooted. Any ideas?