Gmail has the same "problem". This is a concern for you, the person sending mail to these people, because the people you're trying to send mail to are probably going to complain to you about how they're unable to receive your messages.

I know this is just anecdotal, but IME gmail might send you to spam (and seems to at least sometimes learn not to do so for people you have exchanged mail with before) but MS will simply reject all mail from you if you are a small player without a long-standing deditacted /24 without any way for the recipient to get the mail.