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Outlook.com sender requirements

Since May 2025 Microsoft rejects non-compliant mail from high-volume senders to Outlook.com, Hotmail and Live addresses. Here's what it checks.

Who it applies to

Microsoft's rules apply to domains sending more than 5,000 emails per day to its consumer services: outlook.com, hotmail.com and live.com. Business mailboxes on Microsoft 365 are governed by each organisation's own settings.

The requirements

  • SPF must pass for the sending domain.
  • DKIM must pass to validate message integrity.
  • DMARC must be published with at least p=none, and must pass with alignment to the From domain (SPF or DKIM, ideally both).

Microsoft also recommends a functioning From/Reply-To address, an easy unsubscribe link and list hygiene (removing invalid addresses and inactive recipients), but these aren't checked for the rejection.

Error 550 5.7.515

Microsoft announced the rules in April 2025 and, in an update on April 29, 2025, said non-compliant high-volume mail would be rejected from May 5, 2025 instead of first going to Junk. The bounce reads:

550 5.7.515 Access denied, sending domain [SendingDomain] does not meet the required authentication level.

It means at least one of SPF, DKIM or DMARC (with alignment) didn't pass. The usual culprits: a sending service without custom DKIM, so the signature is for the service's domain; a missing DMARC record; or an SPF record over 10 lookups.

Questions

What does 550 5.7.515 mean?

Outlook.com refused your message because your sending domain doesn't meet its authentication requirements for high-volume senders: SPF, DKIM and DMARC must all pass, with DMARC aligned to the From domain.

Does Outlook require one-click unsubscribe?

Microsoft recommends an easy unsubscribe link, but its published requirements for the rejection are SPF, DKIM and DMARC. Gmail and Yahoo do require one-click unsubscribe for bulk marketing mail, so add it anyway.

I send fewer than 5,000 emails a day. Am I affected?

The rejection rule targets high-volume senders. Proper SPF, DKIM and DMARC still improves how all mail is filtered, so it's worth setting up regardless.

Is p=none enough for Outlook.com?

Yes, p=none is the stated minimum, but DMARC must pass — meaning SPF or DKIM must pass for a domain aligned with your From address.

Sources

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