As null__ has implied, this is a function of the e-mail client, not the operating system.
Under Windows in general the usual behavior in an e-mail client that works with multiple accounts is:
1. If you are replying from the unified inbox the reply will have the From: address of the account to which the original message was sent.
2. If you are creating a new message from the unified inbox the default account will be used in the From: field. Some clients will let you select another account if the default is not the account that you wish to send from. If the client does not, see step 3.
3. If you are in any account inbox other than the unified inbox the From: will be the e-mail account for the inbox one is viewing.
Edited by britechguy, 06 July 2018 - 04:41 PM.
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