Permanent failure — do not retry
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.
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 delist@microsoft.com with the NDR.
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.
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
Last reviewed 2026-09-11