Details
This policy setting controls which authentication method Outlook uses to authenticate with Microsoft Exchange Server. Note – Exchange Server supports the Kerberos authentication protocol and NTLM for authentication. The Kerberos protocol is the more secure authentication method and is supported on Windows 2000 Server and later versions. NTLM authentication is supported in pre-Windows 2000 environments.
If you enable this policy setting, you can choose from three different options for controlling how Outlook authenticates with Microsoft Exchange Server:
– Kerberos/NTLM password authentication. Outlook attempts to authenticate using the Kerberos authentication protocol. If this attempt fails, Outlook attempts to authenticate using NTLM. This option is the default configuration.
– Kerberos password authentication. Outlook attempts to authenticate using the Kerberos protocol only.
– NTLM password authentication. Outlook attempts to authenticate using NTLM only.
If you disable or do not configure this policy setting, Outlook will attempt to authenticate using the Kerberos authentication protocol. If it cannot (because no Windows 2000 or later domain controllers are available), it will authenticate using NTLM. The recommended state for this setting is: Enabled:Kerberos/NTLM Password Authentication.
NOTE: When connecting to Office 365, this setting must be set to DISABLED.
Rationale:
Exchange Server supports the Kerberos authentication protocol and NTLM for authentication. The Kerberos protocol is the more secure authentication method and is supported on Windows 2000 Server and later versions. NTLM authentication is supported in pre-Windows 2000 environments.
By default, Outlook will attempt to authenticate using the Kerberos authentication protocol. If it cannot (because no Windows 2000 or later domain controllers are available), it will authenticate using NTLM.
Solution
To implement the recommended configuration state, set the following Group Policy setting to Enabled.
User ConfigurationAdministrative TemplatesMicrosoft Outlook 2013Account SettingsExchangeAuthentication with Exchange Server
Then set the Select the authentication with Exchange server. option to Kerberos/NTLM Password Authentication.
Impact:
The recommended value for this setting in the Microsoft baselines enforces the default configuration, and is therefore unlikely to cause significant usability issues for most users.
Supportive Information
The following resource is also helpful.
This security hardening control applies to the following category of controls within NIST 800-53: Identification and Authentication.This control applies to the following type of system Windows.