Outlook Error 0x80040115: How to Fix RPC Over HTTP Connection Issues

Outlook error 0x80040115 prevents you from connecting to your Exchange server. This error typically appears when using older RPC over HTTP or MAPI over HTTP protocols. It indicates a failure in the underlying network communication layer. This article explains the root cause and provides steps to resolve the connection problem.

Why the RPC Connection Error 0x80040115 Occurs

Error 0x80040115 is a generic RPC server unavailable error. It means Outlook cannot establish a remote procedure call connection to your Exchange server. The most common trigger is a misconfigured or outdated MAPI over HTTP setting in your account configuration.

Modern Exchange servers use MAPI over HTTP as the default connectivity method. If your Outlook client is configured for the older RPC over HTTP protocol or has incorrect proxy server settings, the handshake fails. A corrupted local Outlook profile or OST file can also generate this error code.

Network elements like a corporate firewall, VPN client, or antivirus software can sometimes interfere with the required ports. The error often appears after a Windows update or an Office update changes network security policies.

Steps to Resolve Outlook Error 0x80040115

Follow these steps in order. Start with the profile and account settings before checking system-level configurations.

Method 1: Verify and Update MAPI over HTTP Settings

1. Open Outlook Account Settings
   In Outlook, go to File > Account Settings > Account Settings. Select your Microsoft Exchange account and click Change.
2. Access More Server Settings
   In the Change Account window, click More Settings. Navigate to the Connection tab in the new dialog box.
3. Enable HTTP Connectivity
   In the Connection tab, check the box labeled Connect to Microsoft Exchange using HTTP. Then, click Exchange Proxy Settings.
4. Configure Proxy Settings
   In the Proxy Settings dialog, enter the URL provided by your IT administrator, typically something like outlook.office365.com. Ensure Connect using SSL only and Mutually authenticate the session when connecting with SSL are checked. For Proxy authentication settings, select Basic Authentication. Click OK, then Next, and finish the wizard.

Method 2: Create a New Outlook Profile

1. Open the Mail Control Panel
   Close Outlook. Press Windows key + R, type control, and press Enter. Search for Mail (Microsoft Outlook) and open it. Click Show Profiles.
2. Add a New Profile
   In the Mail dialog, click Add. Enter a name for the new profile, such as Outlook2024, and click OK. The Add Account wizard will launch.
3. Set Up Your Account
   Enter your email address and follow the prompts to configure your Exchange account. Ensure you are connected to the correct network. Once setup is complete, set this new profile as the default to be used when starting Outlook.

If the Error Persists After Configuration

Outlook Still Shows Error 0x80040115 After New Profile

If a new profile does not work, the issue may be system-wide. Open Windows Security and go to Firewall & network protection. Click Allow an app through firewall. Verify that Microsoft Outlook appears in the list and is allowed on both private and public networks. Also check for entries related to Microsoft Office Click-to-Run.

Error Occurs Only on a Specific Network

This points to a network restriction. Try connecting from a different network, like a mobile hotspot, to confirm. If it works elsewhere, contact your network administrator. They may need to open TCP port 443 for HTTPS traffic to your Exchange server endpoints or configure the proxy server correctly.

Outlook Prompts for Password Repeatedly with This Error

Continuous password prompts alongside error 0x80040115 suggest an authentication mismatch. In the Exchange Proxy Settings dialog, try changing the Proxy authentication setting from Basic Authentication to NTLM Authentication. Also, clear your Windows credential cache by searching for Credential Manager in the Windows Control Panel and removing any stored entries for Outlook or Microsoft Office.

RPC over HTTP vs MAPI over HTTP Connectivity

Item	RPC over HTTP (Legacy)	MAPI over HTTP (Modern)
Primary Protocol	Remote Procedure Call wrapped in HTTP	MAPI commands sent directly over HTTP/HTTPS
Connection State	Maintains persistent RPC context	Stateless, connection can be resumed after drops
Default Ports	Requires multiple RPC ports dynamically	Uses only standard HTTPS port 443
Outlook Support	Outlook 2003, 2007, 2010 with updates	Outlook 2013 and later as the default
Network Traversal	More complex for firewalls and proxies	Simpler, behaves like standard web traffic

You can now resolve the Outlook error 0x80040115 by updating your account to use MAPI over HTTP. Creating a fresh Outlook profile is often the fastest solution for persistent connection problems. For advanced configuration, use the Office Customization Tool to deploy pre-configured MAPI over HTTP settings across your organization. Always ensure your Outlook client is updated to the latest version for best compatibility with modern Exchange servers.