Information
This policy setting controls whether users who are joined to a domain in an Active Directory environment can change the primary SMTP address used when setting up accounts in Outlook.
If you enable this policy setting, users cannot change the SMTP settings Outlook retrieves from Active Directory when setting up a new account.
If you disable or do not configure this policy setting, if a user is joined to a domain in an Active Directory environment and does not have an e-mail account configured, Outlook populates the e-mail address field of the New Account Wizard with the primary SMTP address of the user who is currently logged on to Active Directory. The user can change the address to configure a different account, or click Next to use the default settings from Active Directory. The recommended state for this setting is: Enabled.
Rationale:
By default, if a user is joined to a domain in an Active Directory environment and does not have an e-mail account configured, Outlook populates the e-mail address field of the New Account Wizard with the primary SMTP address of the user who is currently logged on to Active Directory. The user can change the address to configure a different account, or click Next to use the default settings from Active Directory.
If users are allowed to change this address, they could incorrectly configure their environment or misrepresent their identity.
Solution
To implement the recommended configuration state, set the following Group Policy setting to Enabled.
User Configuration\Administrative Templates\Microsoft Outlook 2016\Account Settings\Exchange\Automatically configure profile based on Active Directory Primary SMTP address
Impact:
Enabling this setting could prevent users from configuring Outlook as desired in some unusual cases (for example, if Active Directory is temporarily inaccessible during setup). However, most users should experience no significant usability issues.