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DNS Authentication in Mimecast is handled by two separate policies.

DNS Authentication Inbound – Handles whether SPF, DKIM & DMARC checks should apply and what to do when a check if failed.
 DNS Authentication Outbound – Handles DKIM signing your outbound emails through Mimecast.

Both policies require a Definition to be configured first.

 

Inbound Definition

The Definition for Inbound DNS Authentication determines what to do when an SPF, DKIM or DMARC check fails.

  1. Log into your Mimecast Account at https://login.mimecast.com
     
  2. Select Administration Console

  1. Go to ‘Administration > Gateway > Policies’

  1. From the Definitions dropdown, select DNS Authentication Inbound

  1. Select New DNS Authentication - Inbound Checks

  1. Set the name (Description) for the Definition
     
  2. Tick the checkbox next to each check to take place.
     
  3. For each possible result, select the action to take place:
     
     Take No Action: The email will continue to spam checks as normal
     Ignore Managed/Permitted Sender Entries: Any Permitted Sender or Auto Allow policies applying to this email will be ignored.
     Reject: The email is blocked and deleted by Mimecast.
     Honor DMARC Record: Only available for DMARC Fail. Performs the action specified in the sender’s DMARC record:
        Quarantine: The email is held for an Admin to release
        Reject: The email is blocked and deleted by Mimecast

  1. Press Save & Exit

 

Inbound Policy

Once you have created your definition, you will need to create an accompanying policy to determine when it is applied.

  1. Log into your Mimecast Account at https://login.mimecast.com
     
  2. Select Administration Console

  1. Go to ‘Administration > Gateway > Policies’

  1. Click into DNS Authentication - Inbound

  1. Select New Policy

  1. Give the policy a name (Policy Narrative)
     
  2. Set Select Option to definition you created

  1. Set the scope for the policy under Emails From and Emails To

  1. Press Save & Exit

 

Outbound Definition

The Definition for Outbound DNS Authentication determines the DKIM signing settings to use.

  1. Log into your Mimecast Account at https://login.mimecast.com
     
  2. Select Administration Console

  1. Go to ‘Administration > Gateway > Policies’

  1. From the Definitions dropdown, select DNS Authentication - Outbound

  1. Select New DNS Authentication – Outbound Signing

  1. Set the name (Description) for the Definition
     
  2. Tick the checkbox next to Sign outbound email with DKIM
     
  3. Use the Lookup option to select the Domain to use
     
  4. Enter the name for the DKIM Selector
     
  5. Press Generate
     
  6. Add the Public Key as a TXT record with your domain host at the DNS Address
     
  7. Press Check DNS

  1. Press Save & Exit

 

Outbound Policy

Once you have created your definition, you will need to create an accompanying policy to determine when it is applied.

  1. Log into your Mimecast Account at https://login.mimecast.com
     
  2. Select Administration Console

  1. Go to ‘Administration > Gateway > Policies’

  1. Click into DNS Authentication - Outbound

  1. Select New Policy

  1. Give the policy a name (Policy Narrative)
     
  2. Set Select Option to definition you created

  1. Set the scope for the policy under Emails From and Emails To

  1. Press Save & Exit

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