Have just wasted an afternoon on this old issue again, trying all the resolutions I can find. Finally I discovered that the problem lies with the default office 365 install (downloaded from the office.com login) is now 64bit and not compatible with sage 25.1.

Uninstall Office, login to at office.com and use the drop down to select the 32bit version of Office. Emailing from Sage is now working fine, neither program needing elevation. 

Hope this saves someone time, I hadn't twigged the switch to 64bit version, happened in March 2019 apparently.