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Mimecast DKIM Setup

DKIM (DomainKeys Identified Mail) is an email authentication method that uses cryptographic signatures to verify that an email message has not been altered in transit and that it genuinely originates from the stated domain. Implementing DKIM helps protect your domain from spoofing and ensures message integrity.

This guide provides step-by-step instructions to configure DKIM for Mimecast, a cloud-based email management service.

Mimecast DKIM Requirements

To configure DKIM for your domain in Mimecast, follow the steps below. This process helps ensure your email is properly authenticated and protected against spoofing:

  1. Once logged in, click the “Administration” dropdown, select “Gateway” and click “Policies”Mimecast Dkim Screenshot 1
  2. Now click the “Definitions” dropdown and select “DNS Authentication – Outbound“.Mimecast Dkim Screenshot 2
  3. Click “New DNS Authentication – Outbound Signing” to create a new DKIM policy.Mimecast Dkim Screenshot 3
  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”.Mimecast Dkim Screenshot 4
  5. Select your domain by clicking “Select” in front of your chosen domain.Mimecast Dkim Screenshot 5
  6. Select either “1024 bits” or “2048 bits” as your DKIM Key Length. We recommend choosing “2048 bits” for more secure encryption.Click “Generate”.Mimecast Dkim Screenshot 6
  7. Your new DKIM key has been generated successfully.Mimecast Dkim Screenshot 7
  8. Once generated, you can add your DKIM key under domains in Sendmarc if you are a Sendmarc customer or directly in your DNS. Next, under “Policies” select “DNS Authentication – Outbound” by clicking anywhere on the line when highlighted in Blue.Mimecast Dkim Screenshot 8
  9. Add a new Policy for Outbound Signing and use the following values:

    Policy Narrative

    DKIM Outbound

    Select Option:DKIM
    Addresses Based On:Both
    Applies From:Email Domain
    Specifically:[YOURDOMAIN.COM]
    Applies To:Everyone
    Enable / Disable:Enable
    Set priority as perpetual:Always On
    Mimecast Dkim Screenshot 9
  10. Go back into Mimecast and click “Check DNS” to verify that your DNS has been added to your hosting environment successfully.Mimecast Dkim Screenshot 10

How to update your DKIM settings using Sendmarc

Looking to update your DKIM DNS records with Sendmarc? Our easy-to-follow instructions are available here.

Mimecast’s Documentation

For official guidance on configuring DKIM with Mimecast, visit Mimecast’s documentation here.

Looking for SPF Settings?

Find out how to configure your Mimecast SPF settings here.