DKIM uses cryptographic signatures and public-key infrastructure to verify that an email message has not been altered during transit and that it truly came from the claimed sender. Email senders can use DKIM to sign their messages by adding a DKIM-Signature header field to the messages. Email receivers can then use the public key published in the DNS to verify the signature and check that the message has not been tampered with.

DKIM setup for FastMail

You can enable DKIM signing for your domains on FastMail by publishing 3 separate DNS CNAME records, according to FastMail. Remember You must wait for 24-48 hours for your DNS to properly process the changes after publishing the records and saving the changes in your domain’s DNS.

The 3 separate DNS CNAME records include:

You can use Skysnag’s free DKIM Checker to check the health of your DKIM record here

Enable DMARC for your domains to protect against spoofing. Sign up for a free trial today!

For more information on FastMail DKIM setup, you can refer to their reference documentation