What 550 5.7.515 means
Microsoft returns 550 5.7.515 'Access denied, sending domain [domain] does not meet the required authentication level' for mail to its consumer services (Outlook.com, Hotmail.com, Live.com, MSN) when the From domain doesn't pass the authentication Microsoft requires of high-volume senders.
Microsoft defines high volume as 5,000 or more messages a day to its consumer services from the same From domain, and began enforcing the rule in May 2025, first by routing non-compliant mail to Junk and then by rejecting it. The requirement mirrors Gmail and Yahoo's: SPF passes, DKIM passes, and a DMARC record of at least p=none that passes with alignment.
What the bounce looks like
The wording providers document for this code. Your bounce may add an IP address, a session ID or a help link after it.
550 5.7.515 Access denied, sending domain [domain] does not meet the required authentication level.Why cold emailers see 550 5.7.515
- No DMARC record on the From domain.
- SPF or DKIM failing, or passing only for a provider's domain that doesn't align with your From domain.
- Many inboxes on one domain adding up to high volume, even if each inbox sends little.
How to fix 550 5.7.515
- Publish SPF for every service that sends as your domain.
- Enable DKIM signing with your own domain.
- Publish a DMARC record (v=DMARC1; p=none; rua=mailto:...) and confirm messages pass with alignment.
- Send a test to an Outlook.com address and check the Authentication-Results header before resending.
Retry or suppress?
Don't suppress the recipients. Fix authentication and resend; all Outlook.com and Hotmail recipients are affected the same way.
Reading the code
The basic code 550 means "Mailbox unavailable or message refused (permanent)" under RFC 5321. In 5.7.515, the 5 is the class (permanent failure) and the 7 is the subject (security or policy). The detail number 515 isn't in the RFC 3463 / IANA registry; it's specific to the provider, so the text after the code carries the meaning.
- Class 5
- Permanent failure
- Resending the same message won't work. Something about the message, the recipient or the sender has to change first.
- Subject 7
- Security or policy
- A security or policy decision: spam filtering, authentication, blocklists, permissions.
- Detail 5.7.515
- Provider-specific
Check the rest of your setup
Run your sending domain through the SPF, DKIM & DMARC checker to see which record fails, then follow how to set up SPF, DKIM and DMARC. Paste the headers of a test message into the email header analyzer to confirm all three pass.
Got a different bounce? Paste it into the SMTP error code lookup to decode it.