HOWTO: Reverse Lookup Woes

Having issues sending e-mail to big companies such as AOL? Getting undeliverable messages you can't explain?

AOL and many other e-mail providers and ISPs will no longer accept e-mail from SMTP servers that do not have a reverse lookup assigned to them.

You can check to see if your e-mail server has a reverse lookup (PTR Record) assigned to it by bringing up a command prompt in windows and doing 'ping -a ' followed by the external IP address of your e-mail server. (not sure how to find your external IP address? click here)

(a successful reverse lookup)

(an unsuccessful reverse lookup)

Note the two screenshots above. You can see in an unsuccessful reverse lookup, instead of the next line containing a fully qualified domain name (FQDN) followed by the IP in brackets, it simply just contains the IP. This lets you know that there is no reverse lookup record available for the IP you attempted to ping. Note:It is important that you try this test from an external computer, as testing it from inside your network may yield misleading results.

OKAY! Now that we've confirmed that there is no reverse lookup for your IP address, what do we do now? The first step would be to contact your Internet Service Provider and request that your servers external IP address be assigned a reverse lookup record and have them point it to a valid address such as mail.yourcompany.com, which they may need to have created.

(Sometimes, when your DNS hosting is provided by someone other than your ISP, you will need to contact two different companies. Your DNS provider first off to have mail.yourcompany.com created, and then your ISP to have your IP address pointed to that new address.)