Outlook doesn't allow the "+" sign anymore? I can't recieve any e-mail

I've noticed that Outlook.com doesn't recieve e-mails from certain senders where I have the "+" sign in the e-mail. Only a few senders works. This problem just began a few months ago but now it's getting worse. Have outlook.com blacklisted those senders? They are legit.

I don't have them on the blacklist still they won't come through.