Not sure if you can help…
Have you ever had a server that sends emails but the users do not get an email at all. The thing is that the email works except for hotmail/outlook accounts. The email doesn’t even arrive to the junk folder. The server reports the email as sent by it seems that the emails to those accounts are dropped from the outlook(Microsoft) server. The user pool is small, at the moment (less than 200 and no more than 500 for the event). Reading online, it could be a problem with configuring the MX for the server. Do you know anything about that? For instance, here. I am not sure if that is our problem as I am shooting in the dark. Do you happen to know anything about this?