Enhance security for outgoing email (DKIM)

Update DNS records for a subdomain

This article describes how to set up DKIM for a subdomain when your domain provider doesn't let you add TXT records directly to subdomains.

It's common for organizations to use a subdomain to send email. For example, if your domain is solarmora.com, you might send email from a subdomain called mail.solarmora.com

Sometimes you can add a DKIM TXT record directly to the subdomain the same way you do for a domain. However, some domain providers don't let you add TXT records for subdomains. In this case, to use DKIM for the subdomain, add a modified TXT record to the parent domain.

Step 1: Get the TXT record name and value for your domain

Do this step in the Admin console.

  1. Follow the steps in Generate a DKIM key for your domain to get the TXT record name and TXT record value. You can copy these values to a plain text file.
  2. Change the name of the TXT record by adding a period (.) and the name of the subdomain to the end of the TXT record name. 

    The subdomain must be the domain you created the key for. For example, if the subdomain is mail.solarmora.com, change the TXT record to: google._domainkey.mail.

Step 2: Add the TXT record to your domain

Do this step in your domain provider's console or dashboard.

Domain providers have different dashboards and so there are different ways to enter TXT records. With most domain providers, the TXT record name is the first field and the TXT record value is the second field.

  1. Sign in to the management dashboard for your domain.
  2. Locate the page where you update DNS records for your domain.
  3. Add the new DNS record for DKIM:
    • In the first field, enter the TXT record name for the subdomain, for example: google._domainkey.mail.

      Note: Be sure to include the period at the end of the TXT record name.

    • In the second field, enter the value shown in the Admin console, under TXT record value.

      Note: If you get an error when you enter the value, read TXT record value limits.

  4. Save your changes.

TXT record value limits

Some domain providers support a 2048-bit domain key length but limit the size of the TXT record value to 255 characters. In this case, you can't enter the DKIM key as a single text string in the DNS record.

Split the key into multiple text strings that are inside quotes, then enter them together in the TXT record value field. In this example, a long DKIM key is split into two records, and each record is inside quotes:

"k=rsa; p=MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAraC3pqvqTkAfXhUn7Kn3JUNMwDkZ65ftwXH58anno/bElnTDAd/idk8kWpslrQIMsvVKAe+mvmBEnpXzJL+0LgTNVTQctUujyilWvcONRd/z37I34y6WUIbFn4ytkzkdoVmeTt32f5LxegfYP4P/"

"w7QGN1mOcnE2Qd5SKIZv3Ia1p9d6uCaVGI8brE/7zM5c/zMthVPE2WZKA28+QomQDH7ludLGhXGxpc7kZZCoB5lQiP0o07Ful33fcED73BS9Bt1SNhnrs5v7oq1pIab0LEtHsFHAZmGJDjybPA7OWWaV3L814r/JfU2NK1eNu9xYJwA8YW7WosL45CSkyp4QeQIDAQAB"

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