SMTP 550 5.7.606
banned sending IP (Microsoft)
SMTP 550 5.7.606 to 5.7.649 means Microsoft has put your sending IP on its block list. The text reads "Access denied, banned sending IP" and points to sender.office.com. Every message from that IP to Microsoft-hosted mailboxes will fail until the IP is delisted.
Should you remove the address?
Keep the address; fix the sending side
Keep it. The ban is on your IP, not on any recipient.
Block. Retrying changes nothing until the cause on your side is fixed.
How it appears
550 5.7.606 Access denied, banned sending IP [203.0.113.5]. To request removal from this list please visit https://sender.office.com/ and follow the directions.
What causes it
- The IP sent mail that Microsoft's filters judged to be spam.
- The IP was used by a previous tenant or customer with a bad record.
- A compromised server or account on the IP sent spam.
How to fix it
In order — try the first one first.
- Use Microsoft's delist portal at sender.office.com: enter an email address and the blocked IP, confirm the email, then request delisting.
- Allow time. Microsoft says removal can take 24 hours or longer.
- Fix the cause before resuming, or the IP will be listed again.
- If the NDR says 5.7.511 instead, the portal will not work. Microsoft asks you to email [email protected] with the NDR.
Who sends it
Microsoft 365, Exchange Online and Outlook.com.
Microsoft 365
Reply text Access denied, banned sending IP <address>
Microsoft points to its self-service portal for removal requests.
Microsoft 365
Reply text Access denied, banned sender
This is the 5.7.511 text. Microsoft asks you to email [email protected] with the full NDR and IP.
Common questions
- What does SMTP 550 5.7.606 mean?
- SMTP 550 5.7.606 to 5.7.649 means Microsoft has put your sending IP on its block list. The text reads "Access denied, banned sending IP" and points to sender.office.com. Every message from that IP to Microsoft-hosted mailboxes will fail until the IP is delisted.
- Should I retry a 550 5.7.606 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 5.7.606?
- Use Microsoft's delist portal at sender.office.com: enter an email address and the blocked IP, confirm the email, then request delisting.
- Is 550 5.7.606 a hard bounce or a soft bounce?
- 550 5.7.606 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 5.7.606 bounce?
- Keep it. The ban is on your IP, not on any recipient.
- Will verifying my list prevent 550 5.7.606?
- 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 5.7.705 — 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 5.7.515 — authentication required for high-volume senders (Outlook.com)
- 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 Learn: Email non-delivery reports and SMTP errors in Exchange Online
- Source: RFC 3463: Enhanced Mail System Status Codes
Provider wording is quoted only where the provider publishes it.
Last reviewed 2026-10-22