Microsoft 365 5.7.606-649
Access denied, banned sending IP [IP1.IP2.IP3.IP4]
Microsoft 365 5.7.606-649 means: access denied, banned sending IP [IP1.IP2.IP3.IP4]. It is a permanent failure, so do not retry it unchanged. Stop sending from the affected account or IP until the cause is fixed. Check for a compromised account, and remove unverified and unengaged addresses before you resume.
Microsoft 365’s exact wording
Quoted from Microsoft Learn: Email non-delivery reports and SMTP errors in Exchange Online, checked 2026-11-05. Placeholders are Microsoft 365’s own.
Provider's description
Access denied, banned sending IP [IP1.IP2.IP3.IP4]
Possible cause
The IP that you're trying to send from was banned.
Provider's advice
Verify that you're following the best practices for email deliverability, and make sure that your IP's reputations aren't degraded because of compromise or malicious traffic. If you believe that you're receiving this message in error, use the self-service portal to request that your IP address be removed from this list.
| Who sends it | Microsoft 365, Exchange Online and Outlook.com |
|---|---|
| Basic code | Microsoft 365 lists the enhanced code only |
| Enhanced code | 5.7.606: Microsoft 365-specific, not in the IANA registry. Its subject digit puts it under 5.7.0 other or undefined security status. |
| Permanent or temporary | Permanent (5xx) |
| Verifying the list prevents it | Partly |
In practice
550 5.7.606 to 5.7.649 mean the sending IP is banned by Microsoft. They are the codes most often seen by senders on cheap shared IPs and new servers. Microsoft's delist portal lets you request removal of an IP once the cause is fixed. Keep complaint and bounce rates low after delisting, as Microsoft re-lists IPs that relapse. Use the delist portal only after fixing the cause. Until the IP is delisted, every Outlook.com, Hotmail and Microsoft 365 recipient will reject mail from it, so consider moving the affected stream to a different, clean IP or service.
What the sender should do
Stop sending from the affected account or IP until the cause is fixed. Check for a compromised account, and remove unverified and unengaged addresses before you resume.
Would verifying the list have prevented Microsoft 365 5.7.606-649?
Partly
The reply is not only about one address, but providers weigh how often a sender hits addresses that do not exist. Removing bad addresses before sending lowers that signal.
Common questions
- What does Microsoft 365 5.7.606-649 mean?
- Microsoft 365 5.7.606-649 means: access denied, banned sending IP [IP1.IP2.IP3.IP4]. It is a permanent failure, so do not retry it unchanged. Stop sending from the affected account or IP until the cause is fixed. Check for a compromised account, and remove unverified and unengaged addresses before you resume.
- Should I retry after Microsoft 365 5.7.606-649?
- No. It is a permanent (5xx) failure, so the same message to the same address will fail again. Fix the cause first. Stop sending from the affected account or IP until the cause is fixed. Check for a compromised account, and remove unverified and unengaged addresses before you resume.
- Would verifying my list have prevented Microsoft 365 5.7.606-649?
- Partly. The reply is not only about one address, but providers weigh how often a sender hits addresses that do not exist. Removing bad addresses before sending lowers that signal.
Sources
- Microsoft Learn: Email non-delivery reports and SMTP errors in Exchange Online (checked 2026-11-05)
Registry and provider wording is quoted exactly; guidance is written by the SimpleVerifier Team.
SimpleVerifier Team · Last checked against the sources 2026-11-05