When Outlook connects to a slow Exchange server, the Remote Procedure Call (RPC) timeout can cause the application to disconnect or display error messages before the server finishes processing a request. The RPC timeout determines how long Outlook waits for the Exchange server to respond before it abandons the operation. This article explains how to increase the Outlook RPC timeout on Windows 10 and Windows 11 using registry edits and Group Policy, and what limits apply.
RPC timeouts affect tasks like opening large shared mailboxes, sending emails with large attachments, or synchronizing folders on a high-latency network. By extending the timeout, you give the Exchange server more time to complete operations without Outlook disconnecting. You will learn the exact registry keys to modify, the safe range for timeout values, and how to verify the change took effect.
This guide applies to Outlook 2016, Outlook 2019, Outlook 2021, and Outlook for Microsoft 365. The same steps work for both Exchange Online and on-premises Exchange servers, though on-premises servers more commonly trigger timeout issues due to slower hardware or network congestion.