We have recently noticed that Microsoft (owner of Hotmail, Outlook, Live, Office360, etc.) is rejecting all emails originating from our server. That happend for no obvious reason. It’s not possible that some with an Microsoft mail address received a spam message that originates from our server.
You’ll find quite a lot of reports from other server administrators describing the same situation. Also is often hard to get the IP address delisted.
As a workaround we relay all mail to Microsoft owned mail services via another mail server.
But in fact it’s Microsoft responsibility to not rejecting regular mail communication with their customers.
Now it’s your turn: Complain to Microsoft about the rejecting and ask them to delist the IP address 18.104.22.168.