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How to Fix Outlook Won’t Send Emails Error on Windows 10: Step-by-Step Solutions

Outlook is one of the most popular email clients used on Windows 10. However, sometimes users face issues when Outlook won’t send emails. This can be frustrating, especially when you need to communicate quickly.

Fortunately, many common problems causing this error have simple solutions. You do not need to be a tech expert to fix these issues.

This guide will walk you through easy, step-by-step methods to get your Outlook sending emails again. Each step includes clear explanations to help you understand why it matters.

Follow the instructions carefully, starting from the simplest fixes to more advanced options if needed.

Quick Note: Before You Begin

  • Make sure your internet connection is stable and working correctly.
  • Check if your email account login details (username and password) are correct.
  • Ensure that your Outlook application is up to date with the latest updates installed.
  • Verify that your email service (like Gmail, Yahoo, or Exchange) is not experiencing outages.

Step 1: Check Your Outbox and Email Size

Sometimes, emails get stuck in the Outbox. This usually happens when the message is too large or has an attachment that is too big.

  1. Open Outlook and go to the Outbox folder.
  2. If you see the email there, double-click to open it.
  3. Check the size of your email and any attachments. If it’s too large (generally over 20 MB), try removing or compressing attachments.
  4. After reducing the size, try sending the email again by clicking Send.

Why this is important: Large emails or corrupted attachments can prevent Outlook from sending messages. Clearing or resizing helps Outlook process your email smoothly.

Step 2: Confirm Your Email Account Settings

Incorrect email server settings can stop emails from sending. You need to verify that your SMTP (Simple Mail Transfer Protocol) settings are correct.

  1. Open Outlook and click on File > Account Settings > Account Settings.
  2. Select your email account and click Change.
  3. Check the Outgoing mail server (SMTP) address matches your email provider’s recommended settings.
  4. Click More Settings > Outgoing Server tab. Ensure My outgoing server (SMTP) requires authentication is checked.
  5. Go to the Advanced tab and verify the port number and encryption method (usually SSL or TLS) match your provider’s guidelines.
  6. Click OK, then Next, and finally Finish.

Why this is important: SMTP settings tell Outlook how to send your emails through your provider’s servers. Incorrect settings block outgoing emails.

Step 3: Turn Off Work Offline Mode

If Outlook is set to work offline, it won’t send or receive emails. This mode disconnects Outlook from the server.

  1. Open Outlook.
  2. Look at the bottom right corner of the window. If it says Working Offline, this is the problem.
  3. Go to the Send/Receive tab on the ribbon at the top.
  4. Click on Work Offline to toggle it off. The status should change to Connected.
  5. Try sending your email again.

Why this is important: Outlook needs to be connected to the internet to send emails. Offline mode prevents communication with email servers.

Step 4: Clear the Outlook Cache

Sometimes, corrupt cache files affect Outlook’s performance and prevent emails from sending.

  1. Close Outlook completely.
  2. Press Windows + R to open the Run dialog box.
  3. Type %localappdata%MicrosoftOutlook and press Enter.
  4. Find and delete the files with the extension .ost (these are offline Outlook data files).
  5. Restart Outlook. It will recreate these files automatically.
  6. Try sending the email again.

Why this is important: Clearing the cache removes corrupted data that could be blocking email sending processes.

Step 5: Disable Antivirus or Firewall Temporarily

Sometimes, security software blocks Outlook from sending emails. Temporarily disabling your antivirus or firewall can help you check if this is the cause.

  1. Locate your antivirus or firewall icon in the system tray (near the clock).
  2. Right-click on it and choose the option to disable or pause protection temporarily.
  3. Open Outlook and try sending your email again.
  4. If it works, add Outlook as an exception in your antivirus/firewall settings before turning the protection back on.

Important: Only disable your security software briefly and turn it back on immediately after testing to keep your PC safe.

Step 6: Repair Your Outlook Installation

If none of the above solutions work, your Outlook installation might be corrupted. Repairing it can fix internal errors.

  1. Press Windows + I to open Settings.
  2. Go to Apps > Apps & Features.
  3. Find Microsoft Office or Outlook in the list and select it.
  4. Click Modify.
  5. Choose Quick Repair first, and follow the instructions.
  6. If the problem persists, repeat and choose Online Repair (this takes longer but is more thorough).
  7. After repair, restart your computer and try sending emails again.

Why this is important: Repairing fixes damaged program files, restoring Outlook to normal function.

Frequently Asked Questions (FAQs)

Why won’t Outlook send emails but can receive them?

This often happens due to incorrect SMTP settings or blocked outgoing ports. Follow Step 2 to verify your outgoing server details.

How do I know if my email provider is down?

You can check the provider’s status page (e.g., Google Workspace Status Dashboard) or visit websites like DownDetector.

Is there a limit on email size in Outlook?

Yes, Outlook and many email providers limit message size to around 20-25 MB. Large attachments should be compressed or sent via cloud links.

What does SMTP stand for and why is it important?

SMTP stands for Simple Mail Transfer Protocol. It is the protocol Outlook uses to send emails through your email provider’s servers.

Can antivirus software cause Outlook sending problems?

Yes, some security programs may block email traffic. Temporarily disabling them or adding Outlook as an exception often solves the issue.

When Nothing Works

If you have tried all the above steps and Outlook still won’t send emails, consider these final options:

  • Contact your email service provider’s support to check if there are server-side issues or account restrictions.
  • Use the Microsoft Support and Recovery Assistant tool available on the official Microsoft website to diagnose Outlook problems automatically.
  • Consider creating a new Outlook profile: Go to Control Panel > Mail > Show Profiles > Add, then set up your email again.
  • Reinstall Microsoft Office if the repair does not help.

For official help, visit the Microsoft Outlook Support page.

Conclusion

Outlook not sending emails can be caused by many simple issues such as large attachments, incorrect settings, offline mode, or corrupted files. By following the steps from checking the Outbox to repairing Outlook, you can usually fix the problem yourself.

Always start with the easiest solutions and move to advanced fixes only if needed. Regularly updating Outlook and keeping your account settings accurate helps prevent sending issues.

If all else fails, don’t hesitate to reach out to official support or try creating a new Outlook profile. With patience and careful troubleshooting, your emails will be on their way in no time.

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