About DKIM

Question

Hi

We have two different systems, that send out email using our domain, @mathieu.company .com.

Other one of these systems is our Exchange Online, that we use to normal company email. Other system is our infomail system, which send out emails by itself, so there is relay connection to Exchange Online. Infomail is totally separate and different system from Exchange Online and this system's IP is added to our SPF TXT record to allow to send emails using our domain, @mathieu.company .com.

If we enable DKIM in Exchange Online, so that all email sent out from Exchange Online would have encrypted DKIM singature, but we do not enable DKIM signing to our infomail system, would all emails sent out from infomail system get denied/quarantined etc.?

Basically, is DKIM sort of global setting? If we enable it to Exchange Online, will emails sent out from infomail system also get checked agains DKIM?

Answer 1

Correct, if the messages have no DKIM signature, there is no DKIM check.
DMARC is checked if you have a DMARC record however.

If these messages are sent from an authorized IP in your SPF and they are correctly aligned ( FROM header domain matches the RETURN-PATH), then they will pass DMARC

Its always good to have both DKIM and DMARC set of course, but not absolutely required.

Answer 2

No, it would only get checked if the INfoMail emails have a DKIM header signature that references your domain. If they do, then typically you would have a CNAME that refers to the InfoMail domain. If no DKIM signature is added by InfoMail, then it is not checked on those emails.

Answer 3

Ok, so DKIM signature is checked only if email has DKIM signature?

Does DMARC influence somehow on this?

Answer 4

Ok, great, thanks a bunch!