In some small scenarios the administrator install an Exchange Server with two network adapters where one of them is facing the internet and the incoming SMTP traffic start receiving the error 451 4.7.0 Temporary server error. Please try again later.
Note: The scenario depicted above is far from ideal but some small business use such scenario. It is always better to have a Firewall to protect your published servers.
Step 1: Binding order..
Let’s keep the environment neat and for that reason the Active Directory adapter should be the first one listed in the connections. In order to get to that window we need to click on Advanced and then Advanced Settings when listing the network connections on the Exchange Server..
Step 2: Internal Network Adapter..
Since we have two adapters on this host, make sure that the LAN does not have a default gateway and configure the DNS properly pointing out to your local Domain Controller.
Note: It is most likely that if you are using two adapters on Exchange Server you don’t have a network with multiple sites, however if you do you need to add routing to those sites manually.
Step 3: Internet Adapter…
In the adapter that is facing the internet, make sure that the option Register this connection’s address in DNS is unchecked.
In the IP configuration you should have a gateway since you are reaching the SMTP servers on the Internet using that adapter. The DNS settings can be empty or in the IP of your Domain Controllers (not necessary).
Now that we sort it out the network adapters on the server we can perform a inbound SMTP test using our favorite tool (www.EXrca.com) and the error should go away by now.
I’m still getting this error message… what’s next?
Are you still getting this error message, please check your network adapters. It is most likely that the issues lies there.
If you found a different solution, please drop us a line or comment on this post to help other peers of our Exchange Community.