It's now a month, that we can't send email to any Microsoft owned mail domain - for example to hotmail.com or to live.com.
Microsoft is blocking us. We can actually communicate with their first level support staff responsible for the mail servers, however they will neither tell us why we are blocked, nor what we have to do to get unblocked, nor when the block would get lifted.
They propose a whole laundry list of things for us to do - registering with them and constantly maintaining and monitoring our status at some service of theirs. We'd certainly spend half a week to implement those measures and then spend ongoing time to maintain them. But none of that is guaranteed to be of any help.
So if you need to email us then please do not use any of your hotmail accounts for the communication - we unfortunately can not reach you any more.
And it seems we're not the only ones receiving that treatment by Microsoft.