Question : Outgoing email getting rejected on some remote servers - rDNS problem?

The company I work for has Exchange 2003. When I came into the company in August, they had bought a spam filtering service but never configured it correctly. Incoming email is supposed to go through the spam filtering company (Messagelabs) and then come to us. During the process of setting this up, I had to change the Exchange server to not be a open relay. After this happened, I noticed a increase in emails that were not getting sent out.

Looking at the Event Log, most of them are 7010 and 7004 events. I check the logs often, and see half of them just responded with "no such user" etc, which is explainable. But sometimes I get some with the following:

This is an SMTP protocol error log for virtual server ID 1, connection #124. The remote host "", responded to the SMTP command "rcpt" with "554 5.7.1 : Client host rejected: rDNS/DNS_validation_failed._Please_setup_matching_DNS_and_rDNS_records:_http://www.craigslist.org/about/help/rdns_failure xabd-4  ". The full command sent was "RCPT TO:  ".  This will probably cause the connection to fail.

The problem I see with rDNS is that our domain name has a (A) record going to a external web host. Our (MX) records point to Messagelabs. What I suspect is happening is when someone is doing a rDNS on our domain, it is giving them the IP of either our external web host or Messagelabs, not our email servers WAN IP. I'm just wondering what the proper configuration for DNS is in a situation like this is, when you have both MX and A records in different places, and then are sending email out on a different network as well.

Answer : Outgoing email getting rejected on some remote servers - rDNS problem?

Not at all. You just need to make sure the FQDN of your connector is set as an externally resolvable record (ie: you have an A record setup in your domain for it. Something like mail.yourdomain.com is fine). then get a PTR record setup for your IP address to match mail.yourdomain.com.

You should be fine, its a straightforward process.

Shaun