Mimecast is an international company specializing in cloud-based email management.
In order to setup DKIM for Mimecast, it requires a signature to be applied to your emails for which you have to generate a public and private key pair using your Mimecast account. To do this you will have to create an Outbound Signing Definition and an Outbound Policy to apply DKIM to your outbound emails.
Steps to get DKIM set up in Mimecast:
• Setup a definition.
1. Once logged in, click the “Administration” dropdown, select “Gateway” and click “Policies”.
2. Click the "Definitions" dropdown and select "DNS Authentication - Outbound".
3. Click “New DNS Authentication – Outbound Signing” to create a new DKIM policy.
4. Fill in a description and select “Sign outbound mail with DKIM”. A domain needs to be selected and so click “Lookup” next to “Domain”.
5. Select your domain by clicking “Select” in front of your chosen domain.
6. Select either “1024 bits” or “2048 bits” as your DKIM Key Length. We recommend choosing “2048 bits” for more secure encryption.
Do not change the “Selector”. Click “Generate”.
7. Your new DKIM key has been generated successfully.
8. Now you can simply go to your domain's Configuration page in Valimail Enforce and publish the newly created DKIM key.
Click on Add a DKIM key and fill in the info from the newly created Mimecast key and then click Add.
• Setup a policy.
9. Once done with your outbound signing definition, next you need to create your outbound policy.
Under “Policies” select “DNS Authentication – Outbound”.
10. Add a new Policy for Outbound Signing and use the following values:
11. Go back into Mimecast and click “Check DNS” to verify that the Mimecast DKIM key was properly published in Valimail Enforce.
12. After the validation of the DKIM key was done successfully in Mimecast, you can now send DKIM authenticated email for your domain using Mimecast.