Microsoft 365 (Exchange Online) blocked your sending IP because of its reputation. The bounce links to Microsoft's delisting portal at sender.office.com. (Outlook.com / Hotmail blocks use S3140 / S3150-style messages instead.)
Policy rejection · fixable
Common causes
- Spam complaints or spam-trap hits from your IP
- Shared IP used by other senders with bad practices
- New IP with no reputation sending high volume
How to fix it
- Fix the cause (list hygiene, compromised accounts) first
- Request delisting at sender.office.com (the link is in the bounce)
- For Outlook.com / Hotmail blocks (S3150), use Microsoft's sender support form and monitor your IP in SNDS
Blacklist CheckerRun the right check for your domain or paste the full bounce message for a precise explanation.
Open Blacklist Checker →Frequently asked questions
How long does Microsoft delisting take?
Often within a day after the request is approved; repeated listings take longer.