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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.

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 under your domain. For example, if your domain is mydomain.com, you will be editing the DNS records for mydomain.com, not mailout.mydomain.com (although if you wish to use an existing subdomain, you can do this, but it will make things a bit more complex)

The DNS record reference is below. 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. The records to create are as follows. When adding each of these, be sure to enter the subdomain ‘mailout’ in the field provided by your DNS management interface (if you do not enter the subdomain value, then they will apply to your root domain instead, and will be ineffective):

  • 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.

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.

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