Published 2024-08-10 by TechNet New England
Duplicate emails in Outlook are annoying and clutter your inbox. The cause is usually a sync issue, a mail rule, or a configuration problem. ## Common Causes **Multiple accounts pointing to the same mailbox.** If you added the same email account twice (once as Exchange and once as IMAP, for example), you see every email twice. **POP instead of IMAP/Exchange.** POP downloads emails to the device and can re-download them if settings are wrong. **Mail rules or forwarding.** A server-side rule or forwarding configuration may be delivering duplicate copies. **Outlook sync issue.** A corrupt OST file or sync error can cause Outlook to re-download messages. ## Fix 1: Check for Duplicate Accounts 1. Go to **File > Account Settings > Account Settings**. 2. Check the **Email** tab. If you see the same email address listed twice, remove the duplicate. ## Fix 2: Disable POP If Using IMAP or Exchange 1. In Account Settings, check the account type. 2. If you have both a POP account and an IMAP or Exchange account for the same mailbox, remove the POP account. ## Fix 3: Check Rules 1. Go to **File > Manage Rules and Alerts**. 2. Look for rules that forward, copy, or redirect messages. 3. Delete or disable any rules that might create duplicates. Also check server-side rules in webmail (outlook.office.com > Settings > Mail > Rules). ## Fix 4: Rebuild the OST File 1. Close Outlook. 2. Press **Win + R**, type `%localappdata%\Microsoft\Outlook`, press Enter. 3. Find the .ost file for your account and delete it. 4. Reopen Outlook. It will create a new OST file and re-sync from the server. ## Fix 5: Clean Up Duplicates After fixing the cause, clean up existing duplicates: 1. Sort your inbox by **Subject** or **Received** date to group duplicates together. 2. Select and delete the duplicates manually. 3. For large numbers of duplicates, third-party tools like ODIR (Outlook Duplicate Items Remover) can help. Check with IT before installing third-party tools on a managed computer. ## When to Contact IT If duplicates keep appearing after trying the fixes above, the issue may be server-side (a transport rule, a journal rule, or a mailbox migration artifact). Your IT provider can check the Exchange or Microsoft 365 configuration.