Enable RPC encryption
This per-user policy value controls RPC encryption for communication between Outlook 2016 and Microsoft Exchange.
since 0.9.8.11
Purpose
Show registry keys (1)
HKCU\software\policies\microsoft\office\16.0\outlook\rpc\enablerpcencryption
This per-user policy value controls RPC encryption for communication between Outlook 2016 and Microsoft Exchange. It is a REG_DWORD value. A value of 1 makes Outlook use RPC security encryption for applicable Exchange connections and enforces the setting independently of the corresponding Outlook profile option.
The value protects the RPC communication channel. It does not encrypt the email message itself and is not a substitute for S/MIME or Microsoft Purview Message Encryption.
Notes
Security
RPC encryption protects credentials, mailbox data, and message content carried over the RPC channel against straightforward network eavesdropping. With RPC over HTTP, it provides a separate protection layer in addition to any HTTPS encryption applied to the tunnel.
A value of 0, or the absence of the policy value, does not force an unencrypted connection. Outlook defaults and the applicable profile settings then determine whether RPC encryption is used. If the profile permits unencrypted RPC communication, network traffic can be exposed. If the Exchange server requires encrypted RPC connections at the same time, Outlook might be unable to connect to the mailbox.
Notes
This setting applies to RPC-based Exchange connections. It does not control encryption for separate protocols such as MAPI over HTTP. Outlook 2013 SP1 and later versions can use MAPI over HTTP with appropriately configured Exchange servers; this RPC-specific value has no direct effect on such a session. Outlook Anywhere, by contrast, uses RPC over HTTP and is within the scope of the setting.
Microsoft documentation
Microsoft Learn: Microsoft 365 Apps for Enterprise security baseline settings reference
Microsoft Learn: RPC over HTTP Security
Microsoft Learn: MAPI over HTTP in Exchange Server