How to Fix Duplicate Emails in Outlook After IMAP Sync Error

Are you facing duplicate emails in your Outlook mailbox after IMAP sync? No problem, this article will explain and solve how to fix duplicate emails in Outlook after imap sync error using effective manual and automated solutions to handle mailbox performance.

If you're a regular user of Outlook, you may know that duplicate emails can quickly clutter your organised mailbox and reduce Outlook's performance. However, several users are facing this problem right after configuring or syncing an IMAP account. Emails that appear multiple times create duplicates, making it difficult to manage the Outlook mailbox.

However, our guide provides a solution to this problem. Let's walk through our article.

Why Do Duplicate Emails Appear After IMAP Sync?

IMAP Protocols keep your messages synced between the mail server and MS Outlook. This means if any action takes place in Outlook, it will automatically reflect on the server. However, duplicates can easily appear when the syncing process is misconfigured. Here are some more common reasons mentioned below:

1. When your Outlook data file (PST or OST) gets corrupted.
2. Multiple Outlook accounts syncing the same IMAP profile.
3. Server timeouts during the start of the synchronisation process.
4. Wrong sender and receiver settings cause duplicate entries.
5. Unstable network connection during the time of sync.

Let's understand these causes that help you choose the right method to eliminate and avoid duplicates.

Method 1: Manually Delete Redundant Emails

This method is the best way for manual cleanup when your duplicate email volume is low.

Step to Use:

1. Open the affected folder in Outlook (for example, the Inbox).
2. Click on the View tab and choose Change View > Single.
3. Sort emails by Subject or From.
4. Hold the Ctrl key and select the duplicate messages.
5. Press Delete.

This approach gives full control but is time-consuming for large mailboxes.

Method 2: Using an Automated Method

If your mailbox contains thousands of duplicate emails, manual cleanup is impractical. In such cases, a specialized SysTools Outlook duplicate remover tool can scan folders and remove identical messages based on criteria like subject, sender, date, and attachments.

These tools save time and ensure accuracy, especially for business users or large mail archives.

You can read more on the Remove Duplicate Emails in Outlook blog to fix redundant emails in Outlook after IMAP sync.

Method 2: Use Outlook’s Clean Up Tool

Outlook has a built-in Clean Up feature that removes redundant messages in conversations.

Steps to Use:

1. Go to the folder containing duplicates.
2. Click the Home tab.
3. Choose Clean Up > Clean Up Folder.
4. Confirm the action.

Outlook will move unnecessary duplicates to the Deleted Items folder. This works best for conversation-based duplicates, not random repeated messages.

Method 3: Adjust Send/Receive Settings

Improper synchronization intervals can repeatedly download the same emails.

Step to Use:

1. Go to File > Options > Advanced.
2. Click Send/Receive.
3. Select your group and click Edit.
4. Increase the automatic send/receive interval (for example, from 1 minute to 10–15 minutes).
5. Make sure only one send/receive process is running at a time.

Reducing aggressive syncing prevents Outlook from starting a new sync before the previous one finishes.

Method 4: Rebuild the Outlook OST File

For IMAP accounts, Outlook stores emails in an OST file. If this file becomes corrupted, duplicates can appear after IMAP sync.

To rebuild it:

1. Close Outlook.
2. Go to Control Panel and open Mail.
3. Click Data Files and note the location of the OST file.
4. Navigate to that location and rename the OST file (for example, add .old at the end).
5. Open Outlook again.

Outlook will create a new OST file and download fresh data from the IMAP server, often eliminating duplicates.

Method 5: Remove and Re-add the IMAP Account

If duplicates continue, resetting the account can help.

• Backup important data if needed.
• Go to File > Account Settings > Account Settings.
• Select your IMAP account and click Remove.
• Restart Outlook.
• Add the account again using correct IMAP server settings.

This forces a clean synchronization and is one of the most effective ways to fix duplicate emails in Outlook after IMAP sync.

Method 6: Repair Outlook Data File

If you use a PST file (for archived data), corruption can also cause duplication.

Use the Inbox Repair Tool (ScanPST):

1. Quit Outlook.
2. Search for ScanPST.exe on your computer.
3. Open it and browse to your PST file.
4. Click Start to scan and then Repair.

After repair, launch Outlook again and check if duplicates are gone.

Conclusion

Duplicate messages after IMAP synchronization are frustrating but fixable. Whether the cause is a corrupted OST file, incorrect sync settings, or an interrupted download, there is always a reliable solution. Start with simple cleanup methods, then move to rebuilding data files or re-adding the account if needed.

By following the steps above, you can successfully fix duplicate mails on Outlook after IMAP sync and keep your inbox clean, organized, and efficient.