I recently upgraded to Win 10, also installed Office 2016 Pro Plus. My Brother all in one printer scanned to email easily on Win 7, no longer does, Brother could not figure it out. I tried sending to email from Word, get "mapi failure, unspecified error".
Hoping that if I can solve this, scan to email will also work.
I have researched this issue for many hours, can find no solutions that are not old ones, referring to files and directories that do not exist. Tried renaming mapi32.dll (after installing the "take ownership" app.), to no avail. It never gets reinstalled. Tried copying it from a newer laptop, still no joy.

Using Windows Live mail client, set as default in Windows 10.

Most of the posts I can find on the internet regarding the mapi failure are for older systems, this is very new Windows 10, and new Office 2016.

Very disappointed in Microsoft issuing new software that will not work together!