To setup DKIM signing in Mimecast you need to create a definition and a policy

Setting up a definition

  1. Login to Mimecast
  2. Select Administration console
  3. From the top left select Administration > Gateway > policies
  4. Select definitions drop down select DNS Authentication - Outbound
  5. Select New DNS Authentication - Outbound signing
  6. Set a name for the definition
  7. Tick the checkbox Sign outbound mail with DKIM
  8. Use the lookup option to select domain to DKIM sign
  9. Select generate
  10. Create a TXT record within your DNS with the public key provided save and exit
  11. Verify public key in Mimecast console

Setting up a policy

  1. Login to Mimecast
  2. Select Administration Console
  3. From the top left select Administration > Gateway > policies
  4. Search for DNS authentication outbound
  5. Select New Policy
  6. Name the policy
  7. Under emails from use address based on "Both"
  8. Save and Exit

Create a free OnDMARC account to test your configuration.

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