Unfortunately, what Google sees as SPAM might not be the same for Hotmail.. Therefore your emails can easily end up in SPAM with one provider and not with the other. Each mail provider has their own internal filtering methods and most of the time there is very little you can do about it.
You can try to contact Hotmail and explain your situation, but don't hold your breath. Another possible solution is to check the content of your emails and their subject/titles. Many legitimate emails can end up in SPAM/JUNK due to many key words that are flagged by Google, Hotmail, ect..
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