We have an exchange 2003 server. It will quite happily relay smtp for it own subnet. We also have a machine on a DMZ that we need to allow to relay via our exchange server. I have added its subnet 10.0.2.0/255.255.255.0 to the relay 'allow the list below' in the virtual smtp server settings but still it won't relay out. It will accept local addresses firstname.lastname@example.org but not outside addresses 'email@example.com' for example. I have restarted exchange. 'Spoofing' smtp using telnet to port 25 produces the 'cannot relay' type errors. Any ideas please !