How to Setup DKIM for Mimecast?

July 1, 2022  |  3 min read
Mimecast

DomainKeys Identified Mail (DKIM) is a method for email senders to digitally sign email messages in a way that can be verified by email receivers. This allows receivers to verify that the message truly came from the sender, and has not been tampered with. DKIM is intended to address some of the flaws in the existing email system, such as spoofing, phishing, and message tampering. 

Steps to Setup DKIM in Mimecast

  • Open a Mimecast account and log in.
  • Select Gateway > Policies from the menu by going to the Administration submenu.
  • Select DNS Authentication – Outbound from the dropdown menu under Definitions on the Policies page.
  • Click on New DNS Authentication – Outbound Signing to start a new DKIM policy.
  • To set up DKIM for a domain, you must fill out the description box, choose the domain from a lookup list, and give your DKIM selector a name.


If you want a more secure encryption, choose either 1024 bits or 2048 bits under the DKIM length category. Next, select “Generate.”

  • The generation of your DKIM public key for Mimecast was successful. Now all you have to do is visit your DNS registrar and add the DKIM key to the hostname selector.domainkey.yourdomainname.com in your domain’s DNS.
  • You must next establish your outbound policy after finishing your outbound signing definition. Go to Policies > DNS Authentication > Outbound to do this.
  • For your outbound signing, you must add a new DKIM policy using the values listed below:
  • Click on “Check DNS” in your Mimecast account to confirm that your DNS has been added to your hosting environment.

You’re done when you acquire a verified status!

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 Mimecast DKIM setup, you can refer to their reference documentation