Dear community, Is there anyone from the Microsoft 365 team here ? or is there anybody who has contacts of any representative who can help with IP delisting ? We are a cybersecurity company, protecting organizations from our own cloud. Our IP ranges always had a good reputation and all online public services show our IPs as good, and not listed on any spam lists / black lists. We have a customer who is using 149.19.194.91 IP. We checked it into all public services for IP reputation and everywhere it shows up as GOOD. Anyway using Microsoft 365 Services, all emails are rejected: "*Unfortunately, messages from [149.19.194.91] weren't sent.* *Please contact your Internet service provider since part of their network is on our block list (S3150).*" We tried to delist the IP 149.19.194.91 many times through *https://sender.office.com/ <https://sender.office.com/>* but it never worked... All the time we submit the request, it says that it requires escalation, we ask for escalation and nothing happens, we are not getting any feedback for weeks... At the outlook ipStatus(*https://sendersupport.olc.protection.outlook.com/snds/ipStatus.aspx <https://sendersupport.olc.protection.outlook.com/snds/ipStatus.aspx>* ) I don't see any of our IPs having an abnormal status... Has anybody encountered the same issue ? How did you get it resolved ? It looks very hard to cooperate with Microsoft, they keep ignoring us while customer is complaining and the IP was never part of any spam lists/black lists... -- *Best Regards,* Andrian Visnevschi