How to Fix Outlook Error 0x80040115

When using Microsoft Outlook to send or receive emails, you may encounter the error code 0x80040115. This is typically accompanied by the message: “The connection to Microsoft Exchange is unavailable. Outlook must be online or connected to complete this action.” or “We can’t complete this because we can’t contact the server right now.”

This guide provides an in-depth breakdown of what causes this connection failure and how to resolve it on both Windows and macOS using copy-paste terminal commands and system configurations.

1. Understand the Cause of Outlook Error 0x80040115

Error 0x80040115 is a MAPI interface error (MAPI_E_NETWORK_ERROR), which occurs when the Outlook desktop client cannot communicate with the Microsoft Exchange or Office 365 server. The primary root causes include:

• Corrupted OST File: The local Offline Storage Table (.ost) has become corrupted, preventing the synchronization of changes with the mail server database.
• Corrupt Profile Registry Keys: Broken configuration keys within the Outlook profile registry structure cause the client to attempt connection via incorrect protocols or endpoints.
• DNS Resolution Mismatch: Local network DNS servers fail to resolve the Exchange Autodiscover endpoint (autodiscover.outlook.com or local Exchange domain).
• Security Suite Interception: Third-party firewalls or antivirus software with HTTPS/SSL inspection block the secure connection.

Step 1: Force Kill Outlook and Launch in Safe Mode

To ensure no locked threads or corrupt extensions prevent normal operation, terminate Outlook and start it in Safe Mode:

:: Terminate Outlook processes
taskkill /F /IM outlook.exe

:: Launch Outlook in Safe Mode
start outlook.exe /safe

If Outlook launches without the error in Safe Mode, a third-party add-in is the cause. Disable add-ins via File → Options → Add-ins → Manage: COM Add-ins → Go….

Step 2: Clear the Local OST Cache File

Deleting the local .ost cache forces Outlook to rebuild a fresh copy of the mailbox from the Exchange server.

:: Close Outlook first
taskkill /F /IM outlook.exe

:: Rename or delete the OST cache files
del /q /f "%localappdata%\Microsoft\Outlook\*.ost"

Note: A fresh .ost file will be created automatically the next time you open Outlook and sign in.

Step 3: Repair the Office Installation

If core Outlook binaries are corrupted, run the Office Click-to-Run repair utility:

:: Launch Office Quick Repair via Command Prompt (run as Administrator)
"C:\Program Files\Common Files\microsoft shared\ClickToRun\OfficeClickToRun.exe" scenario=Repair platform=x64 culture=en-us ForceRepair=True

(If you are running a 32-bit version of Office on 64-bit Windows, replace C:\Program Files\ with C:\Program Files (x86)\)

Step 1: Force Close Outlook and Clear Local Cache

Close all Office processes and delete the local cached data.

# Force kill Outlook and background helper services
killall "Microsoft Outlook"
killall "Microsoft Outlook Registration Database Daemon"

# Clear the cached profile directories
rm -rf ~/Library/Group\ Containers/UBF8T346G9.Office/Outlook/Outlook\ 15\ Profiles/Main\ Profile/Data/Caches/*

Step 2: Rebuild the Outlook Profile

If clearing the cache is not sufficient, use the built-in Outlook Profile Manager to create a new profile:

1. Open terminal and launch the Outlook Profile Manager:

/Applications/Microsoft\ Outlook.app/Contents/SharedSupport/Outlook\ Profile\ Manager.app/Contents/MacOS/Outlook\ Profile\ Manager

2. Click the Plus (+) button.
3. Enter a new name (e.g., Outlook_Fresh).
4. Select the new profile, click the Gear icon, and choose Set as Default.
5. Launch Outlook and add your email account.

4. Clear DNS Cache and Verify Connectivity

Network configuration issues are a frequent trigger for 0x80040115. Resetting the network stack resolves host-resolution failures.

ipconfig /flushdns
ipconfig /registerdns
netsh winsock reset

# Flush local DNS cache (macOS 10.15+)
sudo dscacheutil -flushcache; sudo killall -HUP mDNSResponder

5. Summary Diagnostics Checklist