Cloudflare network blocked by Microsoft?

upstream (.pamx1-hotmail-com.) error: failed to initialize: Unknown error: permanent error (550): 5.7.1 Unfortunately, messages from [] weren’t sent. Please contact your Internet service provider since part of their network is on our block list (S3150). You can also refer your provider to

How can this be fixed?

You’re using a Microsoft product (e.g. Outlook/Hotmail), and, as you’re indicating that you are looking for a fix, it sounds like you actually want the message that Microsoft is rejecting?

That sounds like they are not living up to your expectations.

Contact Microsoft Support and complain to them about their rejection, and have them adjust their filters.

I get your point of view, however this wasn’t a problem until I migrated e-mail routing to Cloudflare.
Beforehand it was working perfectly.
Also the IP mentioned isn’t mine, it blongs to Cloudflare. Cloudflare needs to fill out a request to get it allowlisted… not me. as I don’t own the IP.

The problem isn’t the IP address being mentioned, the problem is the block list.

The mentioned block list is out of Cloudflare’s hands, so there is nothing Cloudflare can do about it.

The block list also doesn’t cover alone one single IP address, but multiple IP addresses (as per. “part of their network”).

Cloudflare is not the Microsoft user/customer, … you are.

Microsoft is delivering you a service that you are not satisfied with, the complaint about that needs to go to Microsoft, not to Cloudflare.

Microsoft is well known in the email community to be blocking large chunks of IP addresses from time to time, which is causing huge issues for external (i.e. non-Microsoft) parties to deliver messages to them.

If you want to chase a fix for that kind of problem, Microsoft Support is the way forward, because you are their user/customer, and they are causing the problem.

Or, …

Are you willingly supporting a provider that is blocking large parts of the Internet from reaching you?

If not, and Microsoft Support isn’t helpful for you, I would ditch the Microsoft products…