5.7.606 Access denied, banned sending IP [188.8.131.52]. To request removal from this list please visit https://sender.office.com/ and follow the directions. For more information please go to http://go.microsoft.com/fwlink/?LinkID=526655 [eop-APC01.prod.protection.outlook.com]"
Then you know that to request unblocking, you would go to https://sender.office.com/ and fill out the form there to initiate the request. The Office 365 system would then send you a confirmation email, and you'd click on the link in that message to finalize that unblocking request.
If you've attempted this recently, you might have run into trouble. The emails don't seem to be coming through, and so you can't ever finalize any unblocking request, so you can't get your sending IP address removed from their blocking list.
Here's what's going on there. Their system is still alive and kicking. The emails are indeed being sent. Unfortunately, the messages aren't authenticated with a DKIM signature, and they are failing the DMARC authentication check. In other words, those confirmation messages are bouncing off of your spam filter. That's very likely why you're not receiving them.
The fix -- for now -- is an easy one. Use your own personal Hotmail address when filling out the unblocking form on https://sender.office.com/. The confirmation email WILL come through to your Hotmail mailbox, though it will probably end up in the spam folder. Good enough! At least you'll receive it, and be able to click the link and get that sending IP address unblocked.