550 5.7.515: outlook.com high-volume sender authentication
Outlook.com rejected mail from a domain that sends over 5,000 messages a day to it, because the mail did not pass SPF, DKIM and DMARC.
- Microsoft
- Provider
- Permanent (5xx)
- Class
- Sources checked
- Author
At a glance
- Code
- 550 5.7.515
- Temporary or permanent
- PermanentRefused for good: the message comes back to the sender, and resending it gets the same answer.
- Who has to act
- The sender. The fix is on the sending side: your domain, your server or your list.
- What the server says
550 5.7.515 Access denied, sending domain [SendingDomain] does not meet the required authentication level.
What it means
Since 5 May 2025, Outlook.com has required domains that send more than 5,000 messages a day to its consumer addresses to authenticate: SPF must pass, DKIM must pass, and the domain needs a DMARC policy of at least p=none that aligns with SPF or DKIM. Microsoft first announced that failing mail would go to Junk, then changed course before enforcement began and rejects it with 550 5.7.515. Its FAQ adds that a recipient's safe senders list is not honored for this check.
Common causes
- SPF fails for the sending domain, for example because a sending service is missing from the record.
- Messages are not DKIM-signed, or the signature does not verify.
- The domain has no DMARC record, or neither SPF nor DKIM aligns with the From domain.
How to fix it
- 01Check SPF, DKIM and DMARC for the domain with lookup tools and fix any failures.
- 02Make every service that sends as the domain pass SPF and sign with DKIM using the domain.
- 03Publish a DMARC record of at least p=none, and move to a stricter policy once every source aligns.
- 04Read the Authentication-Results header of a test message to an Outlook.com address to confirm all three pass.
Sources
What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.
- Outlook.com Postmaster: Troubleshooting (SMTP error codes)substrate.office.com
- Strengthening Email Ecosystem: Outlook's New Requirements for High-Volume Senderstechcommunity.microsoft.com
- Outlook.com Postmaster: Policies, practices, and guidelinessubstrate.office.com
Related codes
- 5.7.509DMARC failure with a reject policy.The domain in the From address failed DMARC and publishes p=reject, so Microsoft 365 rejected the message as the domain asked.
- 550Mailbox unavailable.The receiving server permanently refused the message for this recipient: the mailbox does not exist, cannot be reached, or the server rejected the message by policy.
Further reading
All 111 Microsoft codesEvery code in the wikiPaste your own bounce