Outlook must use remote procedure call (RPC) encryption to communicate with Microsoft Exchange servers.

Severity	Group ID	Group Title	Version	Rule ID	Date	STIG Version
medium	V-223347	SRG-APP-000575	O365-OU-000002	SV-223347r961878_rule	2025-03-05	3

Description
This policy setting controls whether Outlook uses remote procedure call (RPC) encryption to communicate with Microsoft Exchange servers. If you enable this policy setting, Outlook uses RPC encryption when communicating with an Exchange server. Note: RPC encryption only encrypts the data from the Outlook client computer to the Exchange server. It does not encrypt the messages themselves as they traverse the Internet. If you disable or do not configure this policy setting, RPC encryption is still used by default. This setting allows you to override the corresponding per-profile setting.

Description

This policy setting controls whether Outlook uses remote procedure call (RPC) encryption to communicate with Microsoft Exchange servers. If you enable this policy setting, Outlook uses RPC encryption when communicating with an Exchange server. Note: RPC encryption only encrypts the data from the Outlook client computer to the Exchange server. It does not encrypt the messages themselves as they traverse the Internet. If you disable or do not configure this policy setting, RPC encryption is still used by default. This setting allows you to override the corresponding per-profile setting.

ℹ️ Check
Verify the policy value for User Configuration >> Administrative Templates >> Microsoft Outlook 2016 >> Account Settings >> Exchange >> Enable RPC encryption is set to "Enabled". Use the Windows Registry to navigate to the following key: HKCU\software\policies\microsoft\office\16.0\outlook\rpc If the value for enablerpcencryption is set to REG_DWORD = 1, this is not a finding.

✔️ Fix
Set the policy value for User Configuration >> Administrative Templates >> Microsoft Outlook 2016 >> Account Settings >> Exchange >> Enable RPC encryption to "Enabled".