Fix Outlook Sending Multiple Copies of Emails: Step-by-Step Guide

Vijay Kumar Gupta Cyber Security and Digital Marketing Expert > Blogs > Digital Forensics > Fix Outlook Sending Multiple Copies of Emails: Step-by-Step Guide

Tips to Solve Outlook Sending Multiple Copies of Emails Quickly

Few things are more frustrating than hitting Send in Outlook and realizing the same email has gone out not once, not twice, but five, ten, or even twenty times. Whether it’s a client, a colleague, or your entire mailing list, sending repeated copies of the same message can create confusion, embarrassment, and even damage your professional reputation.

It’s a surprisingly common issue—and thankfully, one that you can fix.

In this comprehensive guide, we’ll break down why Outlook sends the same email multiple times, explore the most reliable methods to stop the behavior, and share pro tips to prevent the issue from returning in the future.

All solutions are beginner-friendly, use short paragraphs for clarity, and walk you through every fix step-by-step.

Why is Outlook Sending the Same Email Multiple Times?

Before applying the solutions, it helps to understand what’s actually causing the issue. Outlook rarely malfunctions without reason—something is creating a loop, a sync error, or a send failure that forces Outlook to keep retrying.

Here are the most common causes:

1. Unstable Internet Connection

A weak or fluctuating connection is one of the biggest triggers for duplicate email sending.

When Outlook tries to send a message and the connection drops mid-process, Outlook doesn’t know whether the email was sent successfully. So it tries again. And again. And again.

The recipient ends up with multiple copies, even though you only clicked Send once.

This especially happens with large attachments, VPN-based connections, or overloaded public Wi-Fi.

2. Corrupted Outlook Data File (PST/OST)

Your Outlook relies on PST or OST files to store emails, settings, and mailbox data.

But if this file becomes corrupted—even slightly—it can create all kinds of strange behavior, including:

  • emails stuck in a send loop
  • duplicates being generated
  • repeated attempts to send the same message
  • slow Outlook performance

Corruption can happen due to abrupt shutdowns, virus infections, system crashes, or oversized mailbox files.

3. Emails Stuck in Outbox

This is by far the most obvious cause.

When an email refuses to leave the Outbox, Outlook interprets it as not sent. So it tries again every time it attempts a send/receive action.

You may see the message sitting there for hours while Outlook keeps trying to resend it.

4. Wrong Account Settings

Incorrect SMTP settings can also cause repeated email sending.

SMTP controls the outgoing mail server. If the port number, encryption type, or authentication method is incorrect, Outlook rejects the “sent” status of your email and resends it.

This is especially common if:

  • You recently changed passwords
  • You switched email hosts
  • You migrated to a new computer
  • You were given outdated server details

5. Third-Party Add-Ins

Add-ins are helpful—until they aren’t.

Security tools, automation extensions, CRM plugins, and spam scanners can interfere with outbound messages. Some accidentally trigger repeat sending by blocking the confirmation that the message was successfully sent.

If Outlook suddenly began misbehaving after installing a new add-in, it’s likely the culprit.

6. Synchronization Errors

Sync failures are extremely common with IMAP accounts, Exchange servers, and systems that access Outlook through multiple devices.

If Outlook is struggling to sync across devices, it may resend emails repeatedly because it can’t confirm which messages were sent and which weren’t.

This can happen when:

  • You use Outlook across phone + laptop + desktop
  • The mailbox is near capacity
  • The server is overloaded
  • Cached Exchange mode is malfunctioning

Proven Methods to Stop Outlook from Sending Multiple Emails

Now that we understand the possible causes, let’s walk through the most reliable ways to fix the issue—quickly, safely, and permanently.

#1. Clear the Outbox

This is the easiest and fastest fix, and it works in a large percentage of cases.

When an email stays in the Outbox, Outlook continuously tries to resend it during every Send/Receive cycle.

Steps to Clear the Outbox:

  1. Open Outlook.
  2. Go to the Outbox folder.
  3. If the message is still there, right-click and choose Delete or Move to Drafts.
  4. Restart Outlook.
  5. If the message refuses to delete, switch Outlook to Work Offline:
    • Go to Send/Receive → Work Offline
    • Try deleting the email again
    • Return online when finished

Once the Outbox is cleared, Outlook stops the send loop immediately.

#2. Fix Corrupted Outlook Data Files

If your PST or OST file is damaged, it can cause duplicate emails, freezing, crashing, or sync failure.

The built-in tool SCANPST.exe can repair many minor errors.

How to Repair the File:

  1. Close Outlook completely.
  2. Search your computer for SCANPST.exe (the Inbox Repair Tool).
  3. Launch the tool.
  4. Click Browse and select your PST or OST file.
  5. Click Start to scan the file.
  6. When prompted, click Repair.
  7. Open Outlook again and check if the issue is fixed.

This helps when the corruption is mild. However, it’s not always effective for large or severely damaged files—those may require an advanced repair method.

#3. Use an Advanced Method to Fix Outlook Sending Multiple Emails

When clearing the Outbox or using SCANPST doesn’t solve the issue, that means the corruption is more complex—or the send/receive mechanism is malfunctioning.

This is where an automated repair method becomes necessary.

An advanced Outlook repair tool (third-party software) can:

  • Repair PST/OST files far more deeply than SCANPST
  • Restore lost emails
  • Rebuild corrupt profiles
  • Fix sync errors
  • Prevent repetitive email sends
  • Improve Outlook performance

Unlike manual fixes, automated repair solutions:

  • Don’t require technical expertise
  • Work faster
  • Avoid the risk of losing data
  • Identify underlying problems that Outlook itself can’t detect

This method is especially recommended if Outlook frequently crashes, freezes, or behaves unpredictably.

#4. Reconfigure SMTP Settings

Incorrect server settings can make Outlook panic and resend messages over and over again.

Every email provider has specific outgoing server settings, and even a tiny mistake—like the wrong port number—can break the process.

Steps to Fix SMTP Configuration:

  1. Open Outlook.
  2. Go to File → Account Settings → Account Settings.
  3. Select your email account.
  4. Click Change.
  5. Verify:
    • SMTP server address
    • Port number (usually 465, 587, or provider-specific)
    • Encryption (SSL/TLS)
    • Authentication method
  6. Click More Settings → Outgoing Server.
  7. Ensure “My outgoing server (SMTP) requires authentication” is checked.
  8. Save changes and restart Outlook.

If you recently changed your password, make sure Outlook has the updated one. Outdated credentials can cause repetitive email attempts as well.

#5. Disable Email Scanning (Antivirus or Firewall Interference)

Some antivirus programs automatically scan outbound emails. In theory, this is a security feature. In reality, it often creates conflict with Outlook’s sending function.

When the antivirus delays or intercepts a message, Outlook thinks the email never left—so it sends it again.

Steps to Disable Email Scanning:

  1. Open your antivirus program.
  2. Look for email protection or outbound scanning features.
  3. Disable or turn off email scanning temporarily.
  4. Restart Outlook and test sending an email.

This doesn’t require turning off your entire antivirus—just the email-scanning portion.

Step-by-Step Guide for the Automated Solution (Advanced Repair)

If you choose to use a professional Outlook repair tool, here’s the typical process step by step:

Step 1: Install and Launch the Tool

Download the software from the official website and install it.

Open the application once installed.

Step 2: Add or Select Your PST/OST File

Most tools will automatically search for Outlook files.
If not, browse manually to locate them.

Step 3: Start the Repair Scan

Click Repair, Scan, or Start depending on the tool interface.

The tool scans for:

  • Corruption
  • Broken folders
  • Sync problems
  • Timestamp errors
  • Send/receive conflict patterns

This scan can take several minutes if the file is large.

Step 4: Preview Recovered Data (Optional)

Many repair tools let you preview the restored items:

  • Emails
  • Attachments
  • Folders
  • Calendars
  • Contacts
  • Tasks
  • Notes

This ensures nothing is missing.

Step 5: Save the Repaired File

Once the repair is complete, save the new PST/OST file.

Most tools allow you to:

  • Replace the old corrupted file
  • Create a new file entirely
  • Export selectively

Step 6: Restart Outlook

Open Outlook and load the repaired profile.
The send/receive feature should now work normally—no more repeated emails.

Bonus Method: Create a New Outlook Profile

If everything fails, your Outlook profile itself might be corrupted or misconfigured.

Creating a fresh profile often solves:

  • Duplicate sending issues
  • Sync failures
  • Broken email rules
  • Add-in conflicts

How to Create a New Outlook Profile:

  1. Close Outlook.
  2. Open the Control Panel.
  3. Click Mail.
  4. Select Show Profiles.
  5. Click Add.
  6. Enter a name for your new profile.
  7. Set up your email account again.
  8. Select “Always use this profile.”
  9. Open Outlook with the new profile.

If the issue disappears after the switch, your old profile was the problem.

Prevent Outlook from Re-Sending the Same Email in the Future

Once you fix the issue, the next step is preventing it from happening again. These proactive habits ensure your Outlook stays stable and error-free.

1. Maintain a Stable Internet Connection

Avoid sending large emails on unstable networks.
Use Ethernet or strong Wi-Fi when dealing with big attachments.

2. Keep Your PST/OST File Under Control

Large mailbox files slow Outlook and increase corruption risk.

Archive old emails regularly.
Empty deleted items.
Compact the mailbox occasionally.

3. Avoid Frequent Forced Shutdowns

Always close Outlook properly.
Do not shut down your computer while Outlook is still processing emails.

4. Update Antivirus and Avoid Over-Scanning

Keep antivirus programs updated.
Turn off email scanning unless absolutely necessary.

5. Update Outlook and Windows

Install updates periodically to fix bugs and improve stability.

6. Avoid Overloading Outlook with Too Many Add-Ins

Disable any add-ins you don’t absolutely need.

7. Back Up Your PST File Regularly

A clean backup makes recovering from corruption much easier.

Conclusion

When Outlook starts sending the same email multiple times, it can feel overwhelming—but it’s a problem that can be solved with the right steps.

From clearing the Outbox to repairing corrupted PST/OST files, adjusting SMTP settings, or fixing sync issues, there are multiple ways to restore your Outlook to normal behavior.

Start with the simplest fixes:

  • Clear Outbox
  • Restart Outlook
  • Check account settings

If the issue persists, repairing your Outlook data file or creating a new profile almost always resolves the problem fully.

By following the preventive steps shared in this guide, you can ensure Outlook runs smoothly and never embarrasses you with repeated emails again.

Digital Forensics

About the Author

Vijay Gupta

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