Came across this today and had to share with others: https://blogs.msdn.microsoft.com/mssmallbiz/2017/07/11/largest-free-microsoft-ebook-giveaway-im-giving-away-millions-of-free-microsoft-ebooks-again-including-windows-10-office-365-office-2016-power-bi-azure-windows-8-1-office-2013-sharepo/

12 that cover parts of Office 365
16 that cover or touch on SharePoint
12 for PowerShell

And many others for Office 2013, 2016, and other office products and many on server products. Sadly there are ZERO on Exchange 😦