DKIM signature is omitted when sender and recipient are controlled by the same organization

[FlorentATo]

Hello,

the document should mention that DKIM signature isn't performed on outbound emails when both the sender's domain and the recipient's domain are controlled by the same organization on Office365.

For example, a company owns multiple domains and has mailboxes setup on them. In that case, even if DKIM is enabled and the sender's DNS zone is properly configured, the recipient will see:

(...)
Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=<sender_domain>;
(...)

For context: I spent quite a bit of time trying to make DKIM work, until is stumbled upon this message: https://answers.microsoft.com/en-us/outlook_com/forum/all/office-365-dkim-not-signing/d7b7bd10-7794-4f47-a055-a3a2ba8ad2b0. I couldn't find this information anywhere else.

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Document Details

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• ID: 249c059f-c3ce-a382-b99e-795a0c1f646a
• Version Independent ID: 5656c114-ae16-6194-cd9f-353b33f4a1e1
• Content: How to use DKIM for email in your custom domain - Office 365
• Content Source: microsoft-365/security/office-365-security/use-dkim-to-validate-outbound-email.md
• Service: microsoft-365-security
• Sub-service: mdo
• GitHub Login: @MSFTTracyP
• Microsoft Alias: tracyp