How to configure a subdomain for transactional SMTP email services

When using transactional email services like Postmark, SendGrid or MailGun (among others), they’ll often ask you to set up a subdomain that they can use as their dedicated sender subdomain. Unfortunately they also often confuse the heck out of their customers by calling it a subfolder or simply not being clear about what they want.

This guide will help you to create the necessary subdomain DNS records that will help ‘authorize’ transactional email providers.

Begin by creating the subdomain with your transactional mail provider. You will need to do this in their panel; if you cannot find the option, please request support from them as we are unable to help you navigate 3rd party systems. To make things simple, we recommend using the subdomain mailout.<yourdomain.com>, but you can use whatever subdomain you wish. We’ll be using mailout as the subdomain throughout this guide, so if you opt to use another subdomain, be sure to replace mailout with your choice of subdomain.

While in their panel, you will want to look for the correct values to set for the DKIM, SPF, RETURN PATH, and DMARC records.

You will now need to create the DNS records. You have two choices as to how to do this:

  1. [Preferred] Simply add them as records under your root domain’s DNS settings. For example, if your domain is mydomain.com, you will be editing the DNS records for mydomain.com, not mailout.mydomain.com
  2. Add the subdomain mailout.<domain> to your hosting control panel (or edit an existing subdomain in your panel), then modify the subdomain’s DNS settings.

We prefer adding the records to the root domain’s DNS settings because you likely won’t be hosting a website on this subdomain and so creating a hosting environment dedicated to this subdomain is unnecessary.

If your DNS is hosted with us and managed by Plesk, this guide will show you how to find and add your DNS records in Plesk.

If you’re doing as we recommended and adding each of these DNS records to your root domain, then you must enter the subdomain ‘mailout’ in the field provided called ‘subdomain’ or ‘host’. If you do not enter the subdomain value, then they will apply to your root domain instead, and will be ineffective for what you want while also being very likely conflict with other records you use for your actual mail service on your domain, so be sure to enter that subdomain value.

  • MX with priority of 15 pointing to mail.<yourdomain.com> (assuming mail.<yourdomain.com> handles your email services. It is when your email is hosted with us)
  • DKIM: record type is TXT
  • RETURN PATH: record type is CNAME
  • DMARC: record type is TXT, use subdomain: dmarc.mailout
  • SPF: record type is TXT

The value to enter for each of these records except the MX record will be provided by your transactional email provider. If you haven’t found them in their panel or documentation, ask them what values they should be set to.

About Jordan Schelew

Jordan has been working with computers, security, and network systems since the 90s and is a managing partner at Websavers Inc. As a founder of the company, he's been in the web tech space for over 15 years.

2 Comments

  1. Kristen on August 19, 2021 at 1:14 pm

    It says you can use an existing sub domain it’s just more complex, any clue as to how?

    • Jordan Schelew on November 3, 2021 at 10:52 pm

      Hey Kristen, If you wish to use an existing subdomain, add those DNS records under the subdomain in your control panel. I’ve reworded the guide to indicate not that it’s more complex, but that adding the subdomain as a hosting environment is unnecessary since you likely won’t be putting a website on the subdomain.

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