The Best Ways to Fix Outlook Sending Duplicate Emails

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Duplicate mails with Outlook.

Issue: Outlook is sending multiple copies of an email to the same recipient.

Root Cause: There are several possible reasons why Outlook keeps on sending duplicate or double emails.

It could be an issue with your inbox settings, a corrupt or outdated Outlook installation, a conflict caused by third-party add-ons, or incorrect mail server settings.

First and foremost, identify the cause of the problem before attempting to fix it. Below is a list of common problems associated with Outlook sending duplicate emails.
  • Your MS Outlook application is integrated with an anti-virus application. Sometimes, due to anti-virus, email is not flagged when sending
  • Outlook is sending duplicate emails because you have set Send/Receive interval time span very short.
  • A slow or non-reliable internet connection can also be one of the possible reasons.
  • Other technical problems: issues in the modem, hub, Wi-Fi, and router. In some cases, especially when you have a slow connection to your mail host, extending the mail server time-out may solve it as well. Resetting your modem, router, hub, WiFi Access Point, and/or other network appliances may sometimes already be the answer too, even when all other network connections seem OK.
  • You have a leave message on the Server option checked, etc.


Resolution: Try the below approaches one by one and find the one that solves your issue:

  1. Disable the anti-virus

If facing Outlook sending multiple emails issue, then this could be because of the anti-virus.

  • To fix it go to settings and disable the anti-virus temporarily. If the problem is resolved by disabling the antivirus then configure it in such a way that it does not interfere with the working of Outlook.

  1. Change the Sending & Receiving interval time

  • Change Send/Receive Interval Time If the Outlook keeps sending duplicate emails. Check the send/receive interval in the Outlook
  • Generally, it is set to 15 minutes by default but if this time span needs to be reduced, then it is possible. In case of consistent downloads, increase the time interval.
  • When the send/ receive interval is set to a very short period and the message takes a while to upload to the mail server, it could be that the next send/receive interval already started before the previous one completes. This will then cause a backlog of Send/Receive tasks that still need to be completed.
  • Open the Send/Receive Progress dialog to see if there is a backlog. Only see up to 2 tasks per mail account in this dialog. When an account is listed more than that, the send/receive interval is too short.

  • To change your Send/Receive interval, go to File > Options > Advanced > Send/Receive… To schedule an automatic send/receive every X minutes, it is recommended not to set it lower than 10 minutes. Try to change that value to 30 minutes.

  1. Update the MS Outlook application

Update Your MS Outlook Application if using an old version of Outlook and this could be the reason why issues with duplicate emails are faced.

  • Update the Outlook application to its latest version.

  1. Disable Add-Ons and plugins

Disable Add-ons and plugins from Microsoft Outlook if using third-party add-ons or plugins with the Outlook application. This could be the reason for duplicate emails.

  • Go to File>Options>Add-ins and then disable all the active add-ons one by one. After that restart Outlook.

  1. Increase the Server Timeout

In some cases, especially when there is a slow connection to the mail host, extending the mail server time-out may solve it as well.

POP3 and IMAP accounts work with Server Timeouts. This tells Outlook when to consider a connection as “lost” when no server response has been received after a configured amount of time.

By default, this is 1 minute. When on a slow or unreliable connection or a connection with high latency (like mobile connections), then it could be that this timeout has been reached. In that case, Outlook will resubmit any message in the Outbox upon the next Send/Receive interval.

When the message was already submitted to the mail server but the acknowledgment was not received before the timeout was reached, the message will be submitted again and thus create a duplicate as well.

Increasing the Server Timeout to 2 or 3 minutes may solve the issue. Directly setting it longer than 3 minutes is not recommended as it often means that the issue lies else where.

  • Outlook 2016 / 2019 / 2021 / Microsoft 365
  1. File-> Account Settings-> Account Settings…
    1. Select your POP3 or IMAP account.
    2. Button: Repair…
    3. Expand: Advanced options
    4. Select: Let me repair my account manually
    5. Button: Repair
    6. Expand section: Outgoing mail
    7. Adjust the slider: Server Timeouts


Increase the Server Timeout when there is a slow or unreliable connection.

  • Outlook 2016 (MSI) / 2013 / 2010
  1. File-> Account Settings-> Account Settings…
    1. Select your POP3 or IMAP account.
    2. Button: Change…
    3. Button: More Settings…
    4. Tab: Advanced
    5. Adjust the slider: Server Timeouts

account-settings-pop3-advanced-server-timeouts-classic.png403×436 9.79 KB

Increase the Server Timeout when you have a slow or unreliable connection.

Besides, resetting the modem, router, hub, WiFi Access Point, and/or other network appliances may sometimes already be the answer too even when all other network connections seem OK.


  1. Another solution to prevent the Robot from sending multiple emails to the same recipient is to implement a check before sending the email. Here are a few suggestions:
  1. Add a check in the workflow to see if an email has already been sent to the recipient within the past 15 minutes. If an email has already been sent, the Robot can skip sending the email again
  2. Use a flag or variable to keep track of when an email was last sent to the recipient. If the flag indicates that an email was sent within the past 15 minutes, the Robot can skip sending the email again. Consider changing the trigger for the job? If the trigger is set to run every 15 minutes, the Robot will send an email every 15 minutes. Consider changing the trigger to run only once per hour, or less frequently, to reduce the number of emails sent
  3. Finally, consider implementing an email management solution that can automatically identify and remove duplicate emails before they are sent. There are several email management solutions available that can help with this, such as Outlook rules, filters, or third-party add-ins
  4. If dealing with a large number of duplicate emails, then it might be worth investing in a third-party tool that can help to quickly identify and delete any duplicates
  5. These tools often have advanced features such as being able to search by date range, sender, subject line, and more, making it easier to find exact duplicates.
  6. Here are few tools that can be tried

  1. Run the Repair Tool for Microsoft Office in UiPath Studio on the impacted Robot machine that is sending the duplicate emails

After performing any steps from above, restart Outlook and check if the problem is resolved. If there is no access to perform the above steps, ask for help internally from the Administrator teams.