Send & Receive Issues

How to Fix Outlook Sending Duplicate Emails with Attachments

Olivia Miller Sep 28, 2026 869 views

Question details

The user needs to stop Outlook from repeatedly sending duplicate messages when an email contains an attachment.

How to Fix Outlook Sending Duplicate Emails with Attachments

Product: Microsoft Outlook
Device & OS: not provided
Scenario: Sending emails with attachments using an IMAP account (such as iCloud) in Outlook.
Observed behavior: Outlook sends the exact same email and attachment multiple times to the recipient instead of sending it just once.

Before you start

Verify with the recipient that they are actually receiving multiple copies of the email, as sometimes IMAP synchronization glitches only cause the email to appear duplicated in your Sent Items folder without sending it twice.

Solution 1Recommended

Test Outlook in Safe Mode and Disable Add-ins

Running Outlook in Safe Mode bypasses third-party add-ins, helping you determine if extensions like Adobe are causing the duplication issue during the sending process.

Third-party add-ins often hook into the email sending process. If an add-in hangs or conflicts while processing an attachment, it can cause the send operation to restart, leading to duplicate emails.

Open Outlook in Safe Mode

Press the Windows Key + R to open the Run dialog box. Type 'outlook.exe /safe' and press Enter to launch Microsoft Outlook in Safe Mode.

Send a Test Email

Create a new email, attach a file, and send it to yourself or a test address. Check if the duplication issue still occurs.

Disable Conflicting Add-ins

If the problem is resolved in Safe Mode, restart Outlook normally. Go to File > Options > Add-ins. At the bottom of the window, select 'COM Add-ins' from the Manage dropdown and click 'Go'. Uncheck third-party add-ins (such as Adobe) and click OK, then restart Outlook.

Test Outlook in Safe Mode and Disable Add-ins

Identifying the Culprit: Disable add-ins one at a time and send a test email after each change to precisely identify which add-in is causing the duplicate sending.

Solution 2

Adjust the Send/Receive Polling Interval

Increasing the automatic send/receive interval prevents Outlook from starting a new sync cycle before a large attachment has finished uploading.

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Frequently Asked Questions

Why does Outlook only send duplicate emails when I include an attachment?

Large attachments take longer to upload to the mail server. If the connection times out, your antivirus intercepts the scan for too long, or the send/receive interval triggers again before the upload finishes, Outlook may restart the process, sending a second copy of the email.

Can my antivirus software cause duplicate sent emails in Outlook?

Yes. Third-party antivirus software that actively scans outgoing emails can significantly delay the sending process. This delay can cause a timeout error in Outlook, prompting it to resend the message, resulting in duplicates. Temporarily disabling email scanning in your antivirus can help diagnose this.

How do I stop iCloud IMAP from duplicating sent items in my Outlook folders?

If emails are duplicating in your 'Sent Items' folder but only arriving once for the recipient, it is an IMAP sync issue. You can fix this by going to File > Account Settings, selecting your iCloud account, clicking 'More Settings', navigating to the 'Advanced' tab, and ensuring 'Do not save copies of sent items' is checked if the server already saves them automatically.

Outlook & Email Problems