You see a ‘Connection to the server was closed by the remote host’ error when Outlook tries to sync your IMAP email. This error stops your emails from downloading and sending. It happens because of a broken connection between Outlook and your email provider’s server. This article explains the common causes and provides steps to restore your email connection.
Key Takeaways: Fixing the Remote Host Connection Error
- File > Account Settings > Server Settings > More Settings > Advanced: Adjusts the server timeout value and SSL/TLS encryption settings to prevent premature disconnection.
- Control Panel > Internet Options > Advanced > Reset: Clears corrupted Windows Internet settings that can interfere with Outlook’s network communication.
- Windows Security > Firewall & network protection > Allow an app through firewall: Ensures Outlook has permission to communicate through the Windows firewall without being blocked.
Why Outlook Loses Connection to Your IMAP Server
The ‘remote host’ is your email provider’s incoming mail server. When it closes the connection, it stops talking to Outlook before the sync job finishes. This is often a timeout issue. Servers are configured to drop idle connections after a set period, usually 30 minutes. If your network is slow or Outlook is processing a large folder, the server may see the delay as inactivity and terminate the link.
Security software is another common cause. Firewalls or antivirus programs that scan email traffic can interrupt the data stream. The server interprets this broken stream as a faulty connection and closes it. Outdated SSL/TLS settings also trigger this. If your email server requires a modern encryption protocol and Outlook is configured for an older one, the security handshake fails, forcing the server to end the session.
How Network Problems Disrupt IMAP
Unstable Wi-Fi or VPN connections create packet loss. The IMAP protocol relies on a steady two-way conversation. When data packets go missing, the server waits for a response that never arrives. After its internal timer runs out, it severs the connection to free up resources. This error can also appear if you are connecting from a new location, as some email providers block sign-ins from unfamiliar IP addresses as a security measure.
Steps to Restore Your IMAP Connection in Outlook
- Increase the server timeout value
Go to File > Account Settings > Account Settings. Select your IMAP account and click Change. Click More Settings, then go to the Advanced tab. Find the ‘Server Timeouts’ slider and move it further to the right, to ‘5 minutes’ or longer. Click OK, then Next, and Finish. - Verify your encryption and port settings
In the same Advanced settings window, check the port numbers. For IMAP, the standard ports are 993 with SSL/TLS or 143 with STARTTLS. Ensure the ‘Use the following type of encrypted connection’ dropdown matches your provider’s requirement, which is typically SSL/TLS or STARTTLS. Using the wrong combination causes an immediate disconnect. - Disable email scanning in your antivirus
Open your antivirus or security suite settings. Look for features named ‘Email Protection,’ ‘Scan incoming email,’ or ‘Scan Outlook.’ Disable these features. This prevents the security software from intercepting and potentially corrupting the data flow between Outlook and the server. You may need to restart Outlook afterward. - Repair the Outlook data file
Close Outlook. Open the Control Panel and go to Mail (Microsoft Outlook). Click Data Files. Select your IMAP account’s data file, which usually has your email address as the name, and click Settings. In the new window, click Compact Now. This process cleans up the local file and can resolve sync corruption. Reopen Outlook and test the connection. - Create a new Outlook profile
If the error persists, the problem may be in your Outlook profile. Close Outlook and open the Control Panel. Go to Mail (Microsoft Outlook) and click Show Profiles. Click Add to create a new profile, name it, and re-add your IMAP email account with the correct settings. Set this new profile as the default to use when starting Outlook.
If the Connection Error Keeps Happening
Outlook Still Shows the Error After Changing Timeout
Contact your email provider or IT support. The server-side timeout may be set lower than what you can configure in Outlook. They can check the server logs for disconnect reasons. Also, ask if there are any IP blocks or security alerts on your account that could be causing automatic disconnections.
Connection Works Briefly Then Fails Again
This pattern suggests a network-level block. Temporarily disable the Windows Defender Firewall to test. Open Windows Security, go to Firewall & network protection, and click ‘Allow an app through firewall.’ Find Microsoft Outlook in the list and ensure both Private and Public network boxes are checked. If you use a third-party firewall, check its application rules.
Error Occurs Only on One Specific Folder
A corrupt email or an overly large folder can cause this. In Outlook, try moving emails out of that problematic folder into a new one you create. If you cannot access the folder, use your email provider’s webmail interface to delete old messages or move them from the troublesome folder. This reduces the sync load.
Manual Configuration vs. Auto Account Setup
| Item | Automatic Setup | Manual Configuration |
|---|---|---|
| Server Discovery | Outlook attempts to find server settings automatically | You must enter the exact IMAP and SMTP server names |
| Port & Encryption | Uses default ports (993/465) | Allows you to specify custom ports and encryption type |
| Error Diagnosis | Limited; generic failure messages | Easier to pinpoint incorrect server or security settings |
| Best For | Major providers like Gmail or Outlook.com | Corporate, custom domain, or older email servers |
You can now diagnose and fix the remote host connection error in Outlook. Start by adjusting the server timeout and verifying your encryption settings in File > Account Settings. If the problem continues, test your connection with email scanning disabled in your antivirus. For a persistent issue, creating a new Outlook profile often provides a clean slate. An advanced step is to use the Test Account Settings feature in the More Settings dialog, which provides a detailed log of the connection handshake for troubleshooting.