In previous post, I described how you can add code to your VSTO/COM add-in to disable your Web Add-in loaded from maniferst via the Office Portal:
Removing Web Add-in Ribbon Customization in Outlook for Windows (theofficecontext.com)

Well with Outlook for Windows, Office 365, version 16.0.13728.36136, you can now disable your Web Add-in via Policy settings.

Download Administrative Template files (ADMX/ADML) and Office Customization Tool for Microsoft 365 Apps for enterprise, Office 2019, and Office 2016 from Official Microsoft Download Center

Here is the path in the policy editor for this setting:

Once in the policy editor, you would set the value. If your OfficeJS Web Add-in has a GUID of {c5bc7737-0d79-4302-9e73-2a614941e914} and the COM add-in is called “My Full Featured Outlook Add-in“, you would set the values like this:

Specifically, the registry key it puts in place is this:

PATH: HKCU\SOFTWARE\Policies\Microsoft\Office\16.0\Outlook\addins\equivalentcomaddin
KEY (string/REG_SZ): {OfficeJS GUID}
VALUE: Prog.ID

For example, if I have an Outlook Web Add-in called “My Outlook Add-in” and it has the following manifest entry:

<?xml version="1.0" encoding="UTF-8"?>
<OfficeApp 
          xmlns="http://schemas.microsoft.com/office/appforoffice/1.1" 
          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
          xmlns:bt="http://schemas.microsoft.com/office/officeappbasictypes/1.0" 
          xmlns:mailappor="http://schemas.microsoft.com/office/mailappversionoverrides/1.0" 
          xsi:type="MailApp">
	<Id>c5bc7737-0d79-4302-9e73-2a614941e914</Id>

Let’s say I have a full VSTO add-in called “My Full Featured Outlook Add-in” and it is registered as the following:

If you were to look at the Policy key after it is set you would have an entry like this:

KEY: {c5bc7737-0d79-4302-9e73-2a614941e914}
VALUE: My Full Featured Outlook Add-in

If it were an older traditional COM Add-in, like the top item: AccessAddin.DC, then it would look like this:

KEY: {c5bc7737-0d79-4302-9e73-2a614941e914}
VALUE: AccessAddin.DC

That is all you have to do if you have the newest builds of Outlook for Windows.

NOTE: Coming later in the year, will be an option to add this entry to your Web Add-in Manifest file the way you can with Excel and Word. 

NOTE: This is all covered in the latest Office add-ins community call.