Exchange Server Cookbook

7.25. Verifying Your External DNS Configuration for Inbound SMTP

Problem

You need to ensure that you have your external DNS properly configured to allow inbound SMTP traffic to your Exchange organization. In addition, you would like to avoid the kind of configuration errors that might cause your outgoing SMTP traffic to be rejected by other hosts.

Solution

Run the following commands from the command line for each server or cluster you intend to receive or send mail outside of your firewall. For outbound hosts, make sure to use the actual external IP address that will be used by your firewall, NAT device, or other SMTP proxy:

               > nslookup 
               <server FQDN> <DNS server hostname or IP address>

> nslookup red-exch01.redmond.3sharp.com ns1.msp.eschelon.com
  Server:  ns1.msp.eschelon.com
  Address:  209.150.200.10

  Name:    red-exch01.redmond.3sharp.com
  Address:  64.65.179.146

> nslookup 
               <server IP address> <DNS server hostname or IP address>

> nslookup 64.65.179.146 ns1.msp.eschelon.com
  Server:  ns1.msp.eschelon.com
  Address:  209.150.200.10

  Name:    red-exch01.redmond.3sharp.com
  Address:  64.65.179.146

> nslookup -q=MX 
               <domain> <DNS server hostname or IP address> > nslookup -q=MX 3sharp.com ns1.msp.eschelon.com Server: ns1.msp.eschelon.com Address: 209.150.200.10 3sharp.com MX preference = 10, mail exchanger = exchange.robichaux.net 3sharp.com MX preference = 20, mail exchanger = relay.salmark.net 3sharp.com MX preference = 30, mail exchanger = relay.thorcom.net 3sharp.com nameserver = ns1.msp.eschelon.com ...