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Martin Front's avatar
Martin Front
Brass Contributor
Nov 27, 2018
Solved

Dkim with multiple domains in Office 365

Hi,   I´m about to implement DKIM and DMARC in to an orginzation with multiple domains (7). Every user uses the same domain name but it´s some shared mailboxes which can have different domain name...
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  • Oliver Moazzezi's avatar
    Oliver Moazzezi
    Nov 28, 2018

    Hi Martin,

     

    No worries, glad I could help. If you did want to run a quick check you can run:

     

    Get-Mailbox |Select DisplayName, GrantSendOnBehalfTo

     

    It should give you an output like in the attached picture.

     

    Take care,

     

     

Oliver Moazzezi's avatar
Oliver Moazzezi
Brass Contributor
Nov 27, 2018

Hi there,

 

You can enable DKIM on select domains yes. You do not have to bulk enable all domains.

 

I am aware of the initial dkim issue for shared mailboxes when the DKIM service was made available in Exchange Online. I believe this is now resolved however. To enable DKIM on a per domain basis simply select 'enable' and ensure you setup the associated CNAME record.

 

More information: https://docs.microsoft.com/en-us/office365/securitycompliance/use-dkim-to-validate-outbound-email

Martin Front's avatar
Martin Front
Brass Contributor
Nov 27, 2018

Hi,

 

Thanks for the answer.

Okej, so DKIM checks will be legit even if you send from a shared malbox?

 

As i understood, sendas should work, sendonbehalf is worse?

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