SMTP 550 5.7.515
authentication required for high-volume senders (Outlook.com)
SMTP 550 5.7.515 is Outlook.com rejecting mail from a high-volume sender that does not meet its authentication requirements. Microsoft requires domains sending more than 5,000 messages a day to Outlook.com, Hotmail and Live addresses to pass SPF, DKIM and DMARC. Fix the records and resend.
Should you remove the address?
Keep the address; fix the sending side
Keep it. This is about authentication.
Block. Retrying changes nothing until the cause on your side is fixed.
How it appears
550 5.7.515 Access denied, sending domain [example.com] does not meet the required authentication level
What causes it
- SPF, DKIM or DMARC is missing or failing for the sending domain.
- DMARC is not published, or does not align with SPF or DKIM.
- A new sending service was added without authentication.
How to fix it
In order — try the first one first.
- Publish SPF for every service that sends as the domain.
- Set up DKIM signing on every sending service.
- Publish a DMARC record, at least p=none, aligned with SPF or DKIM.
- Run a domain audit to confirm all three pass.
Who sends it
Outlook.com, for @outlook.com, @hotmail.com, @live.com and related consumer addresses.
Outlook.com
Reply text 550 5.7.515 Access denied, sending domain <domain> does not meet the required authentication level
Microsoft says it applies when you send 5,000 or more messages to Microsoft consumer services using the same 5322.From domain.
Common questions
- What does SMTP 550 5.7.515 mean?
- SMTP 550 5.7.515 is Outlook.com rejecting mail from a high-volume sender that does not meet its authentication requirements. Microsoft requires domains sending more than 5,000 messages a day to Outlook.com, Hotmail and Live addresses to pass SPF, DKIM and DMARC. Fix the records and resend.
- Should I retry a 550 5.7.515 error?
- No. 550 is a permanent failure, so the message will never be delivered no matter how many times you try. Remove the address — repeated sends to permanent failures are one of the main signals mailbox providers use to throttle a sender.
- How do I fix SMTP 550 5.7.515?
- Publish SPF for every service that sends as the domain.
- Is 550 5.7.515 a hard bounce or a soft bounce?
- 550 5.7.515 is a block rather than a classic hard or soft bounce. The rejection is about your sending (authentication, reputation, content or the recipient's policy), not about whether the address exists. Retrying changes nothing until the cause on your side is fixed.
- Should I remove the address after a 550 5.7.515 bounce?
- Keep it. This is about authentication.
- Will verifying my list prevent 550 5.7.515?
- Not directly. This code is about your authentication, IP or domain reputation, so verification will not lift it. A clean list still matters, because mailbox providers weigh how often a sender hits addresses that don't exist.
Clean the list before the next send.
A bounce report only tells you about the addresses you already mailed. The rest of the list has the same kinds of dead mailboxes in it, and each one becomes a hard bounce recorded against your domain the moment you send.
- A real SMTP mailbox check on every row, before anything is sent
- Dead and mistyped addresses split out, so they never reach your sending tool
- Catch-all, disposable and role addresses flagged alongside
Plans from $9 a month, cancel anytime, no contract. Sign in with Google and your first 100 email checks are free, no card. The free tools stay free either way.
More Microsoft replies: every Outlook and Microsoft 365 SMTP error, and the 550 5.7.515 bulk sender rules.
Other 550 replies
- 550 5.1.1 — mailbox does not exist
- 550 5.7.1 — message refused by policy
- 550 5.4.1 — recipient address rejected, access denied
- 550 5.2.1 — mailbox disabled, not accepting messages
- 550 — mailbox unavailable
- 550 5.1.0 — address rejected, other address status
- 550 5.1.10 — recipient not found (Microsoft 365)
- 550 5.1.8 — bad outbound sender (Microsoft 365)
- 550 5.4.5 — daily sending limit exceeded (Gmail)
- 550 4.4.7 — message expired in the queue
- 550 5.7.25 — no PTR record for sending IP (Gmail)
- 550 5.7.26 — blocked, sender unauthenticated (Gmail)
- 550 5.7.27 — SPF authentication failed (Gmail)
- 550 5.7.28 — unusual rate of unsolicited mail (Gmail)
- 550 5.7.23 — SPF violation (Microsoft 365)
- 550 5.7.124 — sender not in allowed senders list (Microsoft 365)
- 550 5.7.509 — DMARC failed, policy reject (Microsoft 365)
- 550 5.7.606-649 — banned sending IP (Microsoft)
- 550 5.7.705 — tenant has exceeded threshold (Microsoft 365)
- 550 5.7.708 — traffic not accepted from this IP (Microsoft 365)
- 550 5.7.750 — blocked from sending from unregistered domains (Microsoft 365)
- 550 5.7.1 S3140 — IP range on Outlook.com block list
- 550 5.5.0 — Mailbox unavailable (Outlook.com, Hotmail)
- 550 5.7.12 — Sender not authenticated by organization (Microsoft 365)
- 550 5.7.513 — Blocked by the recipient's own block list (Microsoft 365)
Sources
- Source: Microsoft Support: Fix NDR error 550 5.7.515 in Outlook.com
- Source: RFC 3463: Enhanced Mail System Status Codes
Provider wording is quoted only where the provider publishes it.
Last reviewed 2026-10-22