Everything you wanted to know about DNS MX records but were afraid to ask

Email is one of the most popular applications that utilize DNS. Although the web simply uses DNS for linking names to IP addresses for web sites, email servers also require some specialized records above and beyond what is required for basic hostname-to-IP address lookups. For example, when email message is sent from your email client (such as Microsoft Outlook), it can be sent either directly to the target domain or to another email server that is providing a relay service. If your email application specifies an outgoing (SMTP) mail server that is not the final destination server for the message, you're making use of the relay process.

As you may know, an email address is made up of two parts:, a recipient and a host. In the address yourname@yourbusiness.com, 'yourname' is the recipient, the user who will receive the message. This is irrelevant to the SMTP process, though, because the mail transfer agent (MTA) is responsible for making sure that the message gets into the mailbox of the recipient.

The host, '@yourbusiness.com', is of much more interest. In this case, 'yourbusiness.com' refers not to a host in the traditional sense of an 'A' record but rather to a mail server known as a mail exchange (MX). This server is responsible for accepting all mail for 'yourbusiness.com', denoted by a special record - an MX record - in DNS.

A little more information:

Every time you send an email to yourname@yourbusiness.com, DNS is used. Because DNS was built with email in mind (among other things), it has email functionality built right in. Email uses a special type of DNS record known as a mail exchanger (MX) record to facilitate the exchange of email.

SMTP is the protocol used to move mail around the Internet, so it's the Internet equivalent of your friendly neighborhood postal worker. You may have also heard of POP3 and its role in the use of email. Unlike SMTP, POP3 is used only for the retrieval of mail from a mail server and is a minor part of the email process. SMTP, on the other hand, handles all mail duties for email on the Internet until the message reaches its destination server.

After the message has been delivered to the SMTP server, the mail-routing process begins, which is where the DNS mail-enabling features come into play. For each domain serving email to users, such as yourname@yourbusiness.com, is a server known as a mail exchanger. It's responsible for receiving all email destined for that domain.