Email is one of the most important communication mediums to date. We have become dependent on it and since it works so well, we have high expectations that it will work when we need it. But, how does it really work, and what if any role does DNS play in email. First as we discussed in the past, every communication on the Internet depends on DNS, including email. So let’s dig in to what we need to know about DNS and email.

When a user sends an email they are not actually sending the email directly to the recipient. They are, rather, asking their server to take the message and deliver it for them. Once the server accepts the message it tries to deliver it. Here is what, in the simplest manner, the server does. It looks at the envelope and finds the address of the recipients mailbox, for example parisi@yada123.com.

The server then looks at the domain part of the address, everything to the right of the @ sign, yada123.com{dot} and does a DNS lookup. In effect the server asks what are the MX records for yada123.com{dot}? (By the way MX stands for Mail eXchanger, i.e. the server/host responsible/able to receive email for a domain) If DNS is working for that zone, in this example, it should receive an answer of yada123.com{dot} – what – huh? Didn’t we just ask for yada123.com’s address? What is the deal? Well we did, but we asked for the MX records for the domain. As a rule MX records point to A records. So we got back an A record. A records are also called host records, and A records resolve to IP addresses, cool, feels like we are getting closer.

What does the server do now? It needs to ask a second question of the DNS, please (servers are very polite) give me the IP address associated with the A record yada123.com{dot}. In this example the result returned should be 70.120.44.51 – finally, “whoo hoo” an IP address - we can do something with that! The mail server attempts to make a TCP/IP connection to 70.120.44.51 and does so using the SMTP protocol. If all goes well, we won’t get into SMTP details here; the receiving server accepts the message and, again in the simplest of examples, puts it in your mailbox.