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Yes, hotmail will in some instances accept mail at SMTP level and then silently discard it. You cannot even request de-listing.

I had to deal with delivery issues to hotmail (few years ago though) and despite a few hoops, found them pretty reasonable to deal with. Some tools here: https://mail.live.com/mail/services.aspx and https://mail.live.com/mail/troubleshooting.aspx