FortiMail Email Authentication: SPF, DKIM and DMARC

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Domain-based Message Authentication, Reporting & Conformance (DMARC) performs email authentication with Sender Policy Framework (SPF) and DomainKeys Identified Mail (DKIM) checking. 

SPF compares the client IP address to the IP address of the authorized senders in the DNS record. If the test fails, the email is treated as spam.

DKIM allows FortiMail to check for DKIM signatures for incoming email or sign outgoing email with the domain keys for the protected domains.

This recipe covers how to enable DMARC, SPF, and DKIM.

If you require more information on DMARC, SPF, or DKIM, consult the FortiMail Administrator Guide.

Enabling SPF checking

You can enable SPF in the antispam profile and in the session profile settings. If you select to Bypass SPF checking in the session profile, however, SPF checking will be bypassed even though you enable it in the antispam profile. 

To enable SPF in an antispam profile

    1. Go to Profile > Antispam.
    2. Select New or double click an existing profile.
    3. Enable SPF check.

To enable SPF in a session profile

    1. Go to Profile > Session.
    2. Select New or double click an existing profile.
    3. Select the arrow beside the Sender Validation section to expand it.
    4. Enable or disable SPF by selecting the appropriate option from the dropdown menu.

      If the sender domain DNS record lists SPF authorized IP addresses, use SPF check to compare the client IP address to the IP addresses of authorized senders in the DNS record. An unauthorized client IP address increases the client sender reputation score, while an authorized client IP address decreases the client sender reputation score.

 FM SPF

Enabling DKIM checking

 
FortiMail can perform DKIM checking for the incoming mail by query the DNS server that hosts the DNS record for the sender’s domain name to retrieve its public key to decrypt and verify the DKIM signature.
 
To enable DKIM checking
    1. Go to Profile > Session.
    2. Select New or double click an existing profile.
    3. Select the arrow beside the Sender Validation section to expand it.
    4. Enable DKIM check.

Configuring DKIM Signing

 
If you want to sign the outgoing mail with DKIM signatures so that the remote receiving server can verify the signatures, you can do so after you create the protected domains. Note that the DKIM signing settings only appear when configuring an existing protected domain.
 
To configure DKIM signing
 
    1. Go to Mail Settings > Domains > Domains.
    2. Double click an existing protected domain.
    3. Expand the Advanced Settings and then expand the DKIM setting.
    4. Enter a selector to use for the DKIM key in the entry field and select Create.
      The selector name for the key pair appears in the list of domain key selectors. The key pair is generated and public key exported for publication on a DNS server.
    5. Click to select the domain key and then select Download.
    6. Publish the public key by inserting the exported DNS record into the DNS zone file of the DNS server that resolves this domain name.
    7. Select OK.

To enable DKIM signing

    1. Go to Profile > Session.
    2. Select New or double click an existing profile.
    3. Select the arrow beside the Sender Validation section to expand it.
    4. Enable DKIM signing for outgoing messages.
 FM DKIM

Enabling DMARC

DMARC performs email authentication with SPF and DKIM checking. If either SPF or DKIM check passes, DMARC check will pass. If both of them fails, DMARC check will fail.

Enabling DMARC will enable both SPF  and DKIM.

To enable DMARC

  1. Go to Profile > AntiSpam > AntiSpam.
  2. Select New or modify an existing profile.
  3. Enable DMARC check.
 FM DMAC
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