Well lets see, the mail client on Win 10 is rubbish, try importing your email from a different client, yep, no import function.
You can however set up an outlook account and then forward all your email to yourself that way. Creating local folders for email... have not found out how to do this yet, you can create folder on an outlook/exchange account, just not locally.
Contacts is real fun, you can bring you contacts across, however it also has this thing call "people", effectively the same things, however again you can not import you contacts into people. However Mail uses "people" to look up email addresses, not contacts. So, yes, you may have all your "Contacts" there, but they are sod all use.
No migration assistant, given the bloody stupid way MS hides various folders for mail etc, this would be useful.
No target mode, makes upgrading a Mac a doddle when combined with migration assistant.
So, to get a functional Windows box, you have to buy additional software, email spam and so on.
Horrid.