I could use some help getting rid of the <EXCHANGE.xxxx.ad #5.5.0 smtp;550 not local host abc123.com, not a gateway> error. This only occurs when attempting to email 1 specific domain. They say the problem is on my side? They have white listed our domain and are having no problems receiving from anyone else that they are aware of. Any suggestions?
1 Watchguard X1250 Firewall
1 Exchange 2003 server
1 Barracuda Anti-Spam Firewall (only set to block incoming)