If you have your server at home, most likely you have dynamic IP. Many email services, including hotmail, reject email coming from dynamic IP's to combat spam, since most spam comes from these type of servers. To fix this, forward you email through your ISP mail server. I had exact same problem, now that I forward my email through my ISP mail server, I have no problems at all.
You can set this in server-manager/ Configuration/ E-mail.