Information
This policy setting controls whether Outlook is the default program for e-mail, contacts, and calendar services.
If you enable this policy setting, the 'Make Outlook the default program for E-mail, Contacts, and Calendar' check box on the General tab of the Office Center is selected and users cannot change it.
If you disable this policy setting, users cannot make Outlook the default program for these services.
If you do not configure this policy setting, Outlook is made the default program for e-mail, contacts, and calendar services when it is installed, although users can designate other programs as the default programs for these services. The recommended state for this setting is: Enabled.
Rationale:
By default, Outlook is made the default program for E-mail, contacts, and calendar services when it is installed, although users can designate other programs as the default programs for these services. If another application is used to provide these services and your organization does not ensure the security of that application, it could be exploited to gain access to sensitive information or launch other malicious attacks.
If your organization has policies that govern the use of personal information management software, allowing users to change the default configuration could enable them to violate such policies.
Solution
To implement the recommended configuration state, set the following Group Policy setting to Enabled.
User Configuration\Administrative Templates\Microsoft Outlook 2016\Outlook Options\Other\Make Outlook the default program for E-mail, Contacts, and Calendar
Impact:
In most environments that use the Microsoft Office system, Outlook is often already the default program for e-mail, contacts, and calendaring for most users. Therefore, enabling this setting is unlikely to cause usability issues.