A custom subdomain (e.g. mail.example.com or aliases.example.com) is added the same way as a root (apex) custom domain, but you must use different host values in your DNS so the records apply to the subdomain. This article lists the host values for MX, SPF, DKIM (CNAME) and DMARC when adding a subdomain. Start by adding the domain in addy.io; the TXT record for ownership uses the subdomain as the host (e.g. mysub if the subdomain is mysub.example.com).

Host values for a subdomain

Note: If you are adding a subdomain (e.g. mysub.example.com), use the following host values instead of the root domain values

For the MX record: from @ to mysub

For the TXT SPF record: from @ to mysub

For the first CNAME record: from dk1._domainkey to dk1._domainkey.mysub

For the second CNAME record: from dk2._domainkey to dk2._domainkey.mysub

For the TXT DMARC record: from _dmarc to _dmarc.mysub

Replace mysub with your actual subdomain label (e.g. for mail.example.com use mail).

Propagation and checking records

If you have added the records but the domain still is not verifying, wait for DNS propagation (from a few minutes to 48 hours depending on your provider). You can check that the records are visible using mxtoolbox.com or your registrar’s DNS checker.

Keep these records in place for as long as you use the domain on addy.io. A daily check is run on the domain’s records; if any record is removed or changed, the domain may become unverified for sending and you will receive an email notification explaining which record caused it.