I do not know for certain whether this is associated with the update to build dot level 81 or if it was occurring in earlier dot levels of Version 1803, Build 17134 or not, but the Send to->Mail recipient function of Explorer is no longer working correctly.
On my machine, which has Outlook 2010 installed as part of Office 2010, but which has never been my default mail app (which happens to be the Win10 Mail App, which I don't use since I use webmail), is being invoked if I try the above context menu option.
A thread dedicated to this issue is in Windows 10 Support: Setting email program for right-click, send to, mail recipient
I checked on my partner's machine, which is the hardware twin of mine, that's still running Win10 Home, 64-Bit, Version 1709, Build 16299 (can't recall dot right now, but it's the most recent) and the Send to->Mail recipient function works precisely as expected.
Edited by britechguy, 06 June 2018 - 11:05 AM.
Added note about Version 1709 at end.
Brian AKA Bri the Tech Guy (website in my user profile) - Windows 10 Home, 64-Bit, Version 1803, Build 17134
. . . the presumption of innocence, while essential in the legal realm, does not mean the elimination of common sense outside it. The willing suspension of disbelief has its limits, or should.
~ Ruth Marcus, November 10, 2017, in Washington Post article, Bannon is right: It’s no coincidence The Post broke the Moore story