This tip is for all the email server admins out there.

Many mail servers have SPAM filtering options enabled that subject the sending mail server to a battery of DNS tests before accepting any mail. This is an attempt to establish the validity of the claimed identity of the sending server before even beginning a conversation. It’s a bit like looking through the peep hole and sizing up the visitor before deciding if you are going to open the door.In theory, mail servers on the internet should have an Address (A) record, Mail Exchange (MX) record, and a Pointer (PTR) record in DNS. The A record allows us to query the host name of the mail server and get an IP address. The MX record tells us what mail server handles email for the given domain. The PTR record allows us to query the IP address of the mail server and get a host name. A and MX records are pretty universal, while many sites don’t have PTR records or have PTR records belonging to their network provider that don’t match up with their A and MX records.

The good news (from a SPAM filtering perspective) is that a lot of SPAM is sent from mail servers with poorly configured DNS records. Given this fact, doing a few simple checks on a server’s DNS configuration can cut down on SPAM significantly. Unfortunately, some legitimate email servers are also poorly configured and that can lead to problems.

The good news (from your perspective) is that you can avoid looking like a SPAM server by setting up your DNS correctly! Doing so will make it easy for other servers to trust that you are who you say you are.

Here’s a great article on how to ensure that your mail server is setup correctly to avoid looking like a SPAM sending server.

Solving DNS & Email Server Validation Problems

Check back for more tips in the coming days! Please feel free to comment or let me know if you have something you’d like me to cover.