Unable to Send As Attachment From Word, Mapi Errors

Running O365, managing email thru Exchange Admin Center…

When in Word, users are unable to attach Word documents to an email as an attachment using the “send as an attachment” option in Word, see below for steps and error.

Steps to Recreate: Open any World document, then attempt to share: File > Share > Email > Send As Attachment

Error: Word couldn’t send mail because of MAPI failure: “login failure”.

Unfortunately after an hour on the Google I got nothing and fixes that seemed to resolve in the past do not seem to apply to Windows 10?

i.e.

Path of MSMAPI32.dll: C:\Program Files\Common Files\System\MSMAPI\1033

The MSMAP folder/path does not seem to exist anywhere on any of our WIN10 systems?

Appreciate any input or direction…