August 1, 2018

Deliverability 101: FYI about DNS (and subdomains).

Editor’s Note: Today we’re starting a new blog series—Deliverability 101. We brought you the 250ok Deliverability Guide earlier this summer, and we realized we were only scratching the surface. So we’re barrelling head-first into the jungle, chopping away at topics that confuse, bewilder and otherwise agonize those learning how to send good email. We’ll post a new topic every Wednesday, and each will complement our Deliverability Guide. We hope you enjoy the ride.

Domain Name System

We’ll start at the very ground floor: Domain Name System (DNS). DNS is one of the core components of the internet, and without it, you likely wouldn’t be reading this information right now. DNS operates as a translation agent between human-readable words, domain names, and machine-operated internet protocol addresses (IP addresses). But because life can’t be easy, it’s more complicated than just being a translation service. It also allows for the distinction of specific services that might operate on the same server.

How does DNS work?
The DNS translates plain text requests for information into IP addresses for computers to locate, access, and uses information. For example, when a user asks to access, the web browser will ask (via DNS), “Where do I find this website?” DNS will respond, “At the following IP address:”

DNS contains several different types of information based on the request:

  • An address (A) record translates a hostname to an IP address to identify the destination for the requested domain, such as a mail server or website address;
  • A TXT record commonly used as a human-readable note or contact as well as the domain’s authentication policies;
  • An MX record identifying where emails should be sent to for this domain;
  • And several other useful records enable the communication of information between two devices.

Think about it like a sports arena, where the name of the building is published in big, bold letters on the outside of the building (the domain) and the building has many different ticket gates for people attending the event. Each gate is designated for a specific type of attendee, like VIP suite, general access or a balcony, much like the various functions within a domain; www, images, or blog. When you’re walking into the arena, you check your ticket (A record) to identify which gate to enter, and the ticket also tells the gatekeeper whether or not to let you in (like the Mail Exchange (MX) record informing your postmaster). Each of these gates is displayed on a map (DNS record) for the building letting attendees know which door they (site visitors) should be entering through.

Another kind of record is a Canonical or CNAME record for rebranded domains. The record refers to an alias, letting you know that while the domain-owning organization hasn’t changed, the way we refer to it has.

But wait, there’s more! DNS isn’t all about finding information, it’s also about supplying easy-to-look-up information for your domains. Most commonly for email marketers, is the Text (TXT) record used for email authentication, or domain validation with third-party services like Google and Bing, or a service like DocuSign. These records are published as a way to help others validate your infrastructure or prove the domain owner is actually making the requested changes to an indexing system or other secure systems.

Authentication is another large and important part of how DNS is used, but because it is so large, we’ll tackle each kind of email authentication (DKIM, SPF, and DMARC) in later blog posts. They need justice, and we’ve got too much to still talk about right here…


What are they, and why should you care? Well, because they allow for a segregated portion of your brand to operate as if it were an entity of its own. Why would you want to do something like this? Because while is good, it is still restricted to being part of “,” while can operate as a related but separate entity to the original. It could easily be hosted on separate infrastructure, with its own mailing capabilities and authentication. This also works well for email, where a domain owner can assign the use of a subdomain to an email service provider ( and easily manage this as a separate party from their corporate domain, enjoying an entirely different reputation, IPs, authentication, and mail servers.

Working with an ESP that allows for subdomains increases brand affinity with subscribers through brand recognition, allowing for domain alignment (where the sender-from and visible-from are the same domain), which is highly recommended for strong authentication and helps with removing the “sent via” indicator in many email clients. Separate domains permit separate reputations, branding opportunities, and authentication to protect both your marketing and corporate branding.

And that is the lowdown on DNS and subdomains. For more information about deliverability, take a look at the 250ok Deliverability Guide, and check back here regularly for more deep looks at the topics covered there.

PS: A full list of DNS records and their use can be found here.

Author: Matthew Vernhout

Matthew Vernhout is a digital messaging industry veteran and Certified International Privacy Professional (CIPP) with more than a decade of experience in email marketing. Matt is 250ok’s Director of Privacy, and he is currently the Vice Chair of the eec, after serving for several years as the Chair of their Advocacy Subcommittee.

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