No DKIM on Custom Domain via MS365 Family.

Microsoft 365 Family’s Outlook.com personalized-domain service does not provide a supported control for enabling DKIM signing on the custom domain; to obtain DKIM signing for daniellynch.me.uk, move its mail hosting to a service that supports custom-domain DKIM, such as a Microsoft 365 Business plan with Exchange Online.

An accepted Microsoft Q&A answer specifically states that when Outlook.com hosts a custom domain, DKIM records cannot be added through that service and the domain must be moved to another host to obtain custom-domain DKIM ^1^.

Why the business DKIM instructions do not apply

Outlook.com is a consumer service, separate from commercial Microsoft 365 ^2^. A Family subscription does not provide the Exchange Online tenant administration required by Microsoft’s documented DKIM procedure.

The Microsoft 365 custom-domain DKIM process requires:

• A custom domain added to a Microsoft 365 organization.
• Access to the Microsoft Defender portal or Exchange Online PowerShell.
• Two Microsoft-generated DKIM CNAME values.
• Permission to enable the domain through Set-DkimSigningConfig or the Defender portal.

Those are Exchange Online organization controls, not Outlook.com settings ^3^. Therefore, publishing guessed selector1 and selector2 records in your DNS would not enable signing: Microsoft must first provision the corresponding keys and enable signing in the hosting tenant.

Your observed result is consistent with that distinction:

• spf=pass: the sending infrastructure is authorized.
• dmarc=pass: at least one DMARC authentication path is passing and aligned; in this case, that can be SPF.
• dkim=none: the message contains no applicable DKIM signature.

A DMARC pass does not imply that DKIM also passed; DMARC can pass through aligned SPF or DKIM ^4^.

Supported route to DKIM

If DKIM for daniellynch.me.uk is required:

1. Obtain a Microsoft 365 Business plan that includes Exchange Online, or select another mail host that supports custom-domain DKIM.
2. Add and verify the domain in the new mail tenant.
3. Create the users/mailboxes and preserve any required existing mail.
4. Retrieve the exact two DKIM CNAME targets generated for the domain. Do not construct them manually because Microsoft’s format can vary.
5. Publish those CNAME records with your DNS provider.
6. Enable DKIM in: Microsoft Defender portal → Email & collaboration → Policies & rules → Threat policies → Email authentication settings → DKIM.
7. Change the domain’s MX and other provider-specific DNS records as directed by the new host.
8. Send an external test message and verify that its headers show dkim=pass, with the DKIM d= domain aligned to daniellynch.me.uk.

For Exchange Online, the relevant administrative check is:

Get-DkimSigningConfig -Identity daniellynch.me.uk |
    Format-List Name,Enabled,Status,Selector1CNAME,Selector2CNAME

Set-DkimSigningConfig -Identity daniellynch.me.uk -Enabled $true

Run the enable command only after publishing the exact CNAME values returned for the domain ^3^.

Important migration warning

Existing Outlook.com personalized addresses can continue operating, but Microsoft stopped allowing Microsoft 365 Personal and Family customers to create new personalized addresses after November 30, 2023. If an existing personalized address is removed, it cannot be added back to Outlook.com afterward ^5^.

Do not remove the current Outlook.com personalized address until the new mailboxes, DNS records, historical-mail migration, and cutover plan are ready. The practical choices are therefore:

• Keep the legacy Outlook.com setup with SPF-aligned DMARC but without configurable custom-domain DKIM; or
• Migrate the domain’s mail hosting to Exchange Online or another DKIM-capable provider.

References

1. how to assure my outgoing emails are delivered (not sent to spam) - Microsoft Q&A
2. Subscription features in Outlook.com for Microsoft 365 subscribers
3. Set up DKIM to sign mail from your cloud domain
4. Fix NDR error "550 5.7.515" in Outlook.com | Microsoft Support
5. Changes to Microsoft 365 email features and storage | Microsoft Support