PMTA Dual DKIM

[Underground Forum]

Configuring dual DKIM in PowerMTA​

By default, PowerMTA supports the ability to add a second DKIM-Signature header.

To configure double DKIM, open virtualhost.txt

<virtual-mta TEST-vmta>

domain-key dkim1,DOMAIN-1.com,/etc/pmta/dkim1.DOMAIN-1.com.pem # First key, dkim1 - key selector
domain-key dkim2,DOMAIN-2.com,/etc/pmta/dkim2.DOMAIN-2.com.pem # Second key, dkim2 - key selector

max-smtp-out 850
    <domain gmail.com> # Settings for Gmail
     dkim-headers Feedback-ID
     second-dkim-headers Feedback-ID # Add second DKIM in Feedback-ID
    </domain>
    <domain *> # Settings for all email providers
     dkim-sign yes
     second-dkim-sign yes # Enable second dkim
     second-dkim-identity @DOMAIN-1.com # Select first domain as identity
    </domain>
</virtual-mta>

PMTA will add Feedback-ID header to the both signatures only for Gmail and both keys (dkim1 and dkim2) for all other email providers.

All Second-DKIM directives​

second-dkim-add-body-limit
second-dkim-add-timestamp
second-dkim-algorithm
second-dkim-body-canon
second-dkim-disallow-adding-headers
second-dkim-expire-after
second-dkim-headers
second-dkim-headers-canon
second-dkim-identity
second-dkim-identity-fallback
second-dkim-sign
second-dkim-query-method

 

[atonisprio]

what is the purpose of this?

 

[D•Jass]

what is the purpose of this?

In some cases it can be used for better email deliverability.