Office 2016: Disallow sign-in to Office, but continue using Office 365 email in Outlook

Add the following registry key: HKCU\SOFTWARE\Microsoft\Office\16.0\Common\Identity\EnableADAL=0

This disables Modern Authentication on your home computer, which is what is causing your home Office/Outlook to log in all together in one shot.

You wish to use the work account only on Outlook, but for Microsoft this means a login on all Office products.

I assume that the account details are stored in the registry, so your problem is running Outlook with these registry entries, but the rest of Office without.

A simple solution to this problem is to use Sandboxie, which creates a virtual environment for selected programs, where all file and registry updates are diverted to some disk storage which is called the sandbox. This means that these updates do not exist for programs that are not started via Sandboxie and outside the sandbox.

This way you could start Outlook via Sandboxie and logon to your work account once and for all. The other Office applications you will start directly, not through Sandboxie, so they do not use your work account, and you may even logon to your personal Outlook account.

Thus Outlook will have two launch modes, sanboxed or not, each using a different account.

You can create a desktop shortcut that will launch Outlook directly inside the sandbox, to simplify its use. See the Sandboxie FAQ of Windows Shell Integration.

The free version of Sandboxie is limited to only one sandbox. However, for $34.95 you can have an unlimited lifetime license. (Edit: Sandboxie is now freeware.)

To make Outlook work in the sandbox, I have set the Email the following settings of Sandboxie :

Email Reader

Internet Access