We just recently setup a new SBS 2008 server and exchange 2007. After some messing around it seemed like we had the email working and everything was fine. Today I have received a couple of NDR's that staff have received when trying to send to a domain. It is coming back saying they have rejected our message because #550 5.7.1 Client host rejected: cannot find your hostname, [126.96.36.199] ##
The 188.8.131.52 is the public IP address that I setup on the sonicwall and everyone in the office gets that IP address when they do lookup of the public ip (whatismyip.com). Our MX record points to 184.108.40.206. I have the rules setup in the sonicwall to allow SMTP traffic to flow from the 220.127.116.11 to the exchange server and everything looks good except for the NDR's.
Before this upgrade we had a Pix firewall and when doing an IP check on the old server you would get the IP address of the MX record. I want to try and eliminate these NDR issues so I am trying to figure out how I can get the 18.104.22.168 to show up on outbound messages so the hosts are able to find the correct MX record and process the email.