Troubleshooting Outlook: Fixing Email Sending Issues in Windows (With & Without Attachments)

Table of Contents

• Common Scenarios: Identifying the Scope of the Problem¶
• Troubleshooting Steps to Fix Outlook Email Sending Issues¶

While Microsoft Outlook stands out as a robust and feature-rich email client, users occasionally encounter operational hiccups. Among these, the inability to send emails, either with or without attachments, is a particularly frustrating problem for Windows users. This issue can stem from a multitude of factors, creating a complex troubleshooting landscape. Before diving into specific solutions, it’s crucial to remember the fundamental aspect of email attachments: size limits. Email service providers impose restrictions on attachment sizes to ensure smooth operation and prevent server overload. Being mindful of these limits, as detailed by your specific email service, is the first step in diagnosing sending problems.

This article aims to provide a comprehensive guide to resolving email sending issues in Outlook on Windows 11 and Windows 10. Whether you are facing difficulties with sending simple text emails or emails with attachments, the following solutions cover a range of potential causes and offer step-by-step instructions to get your Outlook back to sending emails reliably.

Common Scenarios: Identifying the Scope of the Problem¶

Before implementing solutions, it’s helpful to pinpoint the exact nature of the problem. Understanding the specific scenario can guide you to the most effective troubleshooting steps. Here are a few common situations users encounter:

• Outlook Emails Not Sending on One Device, But Working Elsewhere: You might find that Outlook is unable to send emails on your primary Windows PC, yet functions perfectly on your smartphone or another computer. This often indicates a problem specific to the Outlook installation or settings on the affected PC, rather than a broader account issue.
• Intermittent Sending Issues: Emails might send successfully sometimes, but fail at other times. This can be harder to diagnose, but could point to temporary network glitches, server-side problems, or even conflicts with other software running on your computer.
• Specific Error Messages: Outlook may display error messages when sending fails. Note down these error messages precisely, as they often provide valuable clues about the underlying cause. Error codes or descriptive text can significantly narrow down the troubleshooting process.
• Problems Sending Only with Attachments: If you can send emails without attachments but encounter failures when including files, the issue might be related to attachment size limits, file type restrictions, or problems with Outlook’s attachment handling.
• Emails Stuck in Outbox: Drafted emails might appear to send but remain stuck in your Outlook Outbox folder. This usually signals that Outlook is unable to connect to the outgoing mail server or that there is an issue preventing the emails from being processed for sending.

Isolating the scenario that matches your experience is the initial step toward targeted troubleshooting. Now, let’s explore various solutions to get your Outlook sending emails again.

Troubleshooting Steps to Fix Outlook Email Sending Issues¶

Here are several methods to troubleshoot and resolve Outlook email sending problems in Windows. Proceed through these steps systematically, testing after each solution to see if the issue is resolved.

1. Repair Your Outlook Profile¶

Outlook profiles can sometimes become corrupted, leading to various malfunctions, including email sending problems. Repairing your Outlook profile can often resolve these underlying issues by rebuilding the profile’s data files and settings. This process is generally safe and does not delete your emails or account information.

Steps to Repair Your Outlook Profile:

1. Open Microsoft Outlook: Launch the Outlook application on your Windows PC.
2. Navigate to File Tab: In the Outlook ribbon, click on the “File” tab located in the top left corner.
3. Access Account Settings: Within the File menu, under the “Info” section, find and click on “Account Settings.” In the dropdown menu that appears, click on “Account Settings” again.
4. Select Problematic Account: In the Account Settings window, you will see a list of your email accounts configured in Outlook. Select the specific email account that is experiencing sending issues.
5. Initiate Repair: With the account selected, click on the “Repair” button located above the account list.
6. Review and Proceed: The “Repair Account” dialog box will appear. Review the account settings displayed to ensure they are correct. Typically, Outlook will automatically detect and pre-fill the necessary settings. Click “Next” to proceed with the repair process.
7. Follow On-Screen Prompts: Outlook will then attempt to repair your account. Follow any on-screen instructions or prompts that appear during the repair process. This might involve testing your account settings or restarting Outlook.
8. Test Email Sending: Once the repair process is complete, restart Outlook and attempt to send a test email to verify if the issue has been resolved.

If repairing the profile does not fix the problem, move on to the next troubleshooting step.

2. Turn Off “Work Offline” Mode¶

Outlook’s “Work Offline” mode is a useful feature that allows you to browse your emails, compose messages, and manage your calendar without an active internet connection. However, if “Work Offline” is inadvertently enabled, Outlook will not attempt to send or receive emails. Emails composed in offline mode will remain in your Outbox until the mode is disabled.

Steps to Disable “Work Offline” Mode:

1. Open Outlook: Launch the Outlook application.
2. Go to Send/Receive Tab: In the Outlook ribbon, click on the “Send / Receive” tab.
3. Check “Work Offline” Status: Locate the “Work Offline” button in the “Preferences” group on the Send/Receive tab.
4. Disable if Enabled: If the “Work Offline” button is highlighted or appears to be pressed (indicating it’s active), click on it to disable “Work Offline” mode. When disabled, the button should appear normal and not highlighted.
5. Check Outbox: After disabling “Work Offline,” check your Outbox folder. If there are emails stuck there, Outlook should now attempt to send them.
6. Test Email Sending: Send a test email to confirm that Outlook is now sending emails correctly with the “Work Offline” mode disabled.

Ensure “Work Offline” mode is consistently turned off, especially if you frequently switch between online and offline work.

3. Increase Outlook Attachment Size Limit (Registry Edit)¶

Outlook has a built-in limitation on attachment sizes, which is often set slightly lower than the maximum attachment size allowed by your email service provider. This is designed to prevent sending extremely large files that could clog email servers. However, in some cases, this default limit might be too restrictive. You can increase the attachment size limit by modifying the Windows Registry. Caution: Editing the Registry incorrectly can cause serious problems. Follow these instructions carefully. It’s recommended to back up your Registry before making changes.

Steps to Increase Attachment Size Limit via Registry Editor:

1. Open Registry Editor: Press the Windows key + R to open the Run dialog box. Type regedit and press Enter. Click “Yes” if prompted by User Account Control.

2. Navigate to the Correct Path: In the Registry Editor window, navigate to the following path based on your Outlook version using the folder tree in the left pane:

   • Outlook 2021, 2019, and 2016: HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\Preferences
   • Outlook 2013: HKEY_CURRENT_USER\Software\Microsoft\Office\15.0\Outlook\Preferences
   • Outlook 2010: HKEY_CURRENT_USER\Software\Microsoft\Office\14.0\Outlook\Preferences

3. Create “Preferences” Key if Missing: If the “Preferences” key (folder) does not exist under the “Outlook” key, you need to create it. Right-click on the “Outlook” key, select “New” > “Key,” and name the new key “Preferences.”

4. Create “MaximumAttachmentSize” DWORD Value: In the right pane of the Registry Editor, right-click in an empty space, select “New” > “DWORD (32-bit) Value.” Name the new DWORD value MaximumAttachmentSize.
5. Modify “MaximumAttachmentSize” Value: Double-click on the newly created MaximumAttachmentSize DWORD value to open its Edit dialog.
6. Set Value Data:
   • Under “Base,” select “Decimal.”
   • In the “Value data” field, enter the maximum attachment size you want to allow in kilobytes (KB). For example, to set the limit to 25MB, enter 25600 (since 1MB = 1024KB, and 25MB = 25 * 1024 KB = 25600 KB). Choose a value that is within the limits of your email provider.
7. Click “OK”: Click “OK” to save the changes.
8. Close Registry Editor: Close the Registry Editor.
9. Restart Outlook: Restart Microsoft Outlook for the changes to take effect.
10. Test with Attachments: Try sending an email with an attachment that previously exceeded the limit to see if the issue is resolved.

Remember to set a reasonable attachment size limit that is within the bounds of your email service provider’s restrictions. Setting an excessively large limit might still result in sending failures if the email provider rejects emails larger than their allowed size.

4. Check Mailbox Settings¶

Incorrect or outdated mailbox settings for your email account in Outlook can lead to sending problems. Verifying and, if necessary, resetting or adjusting your mailbox settings can resolve issues related to server connections, port numbers, and encryption methods.

Steps to Check and Adjust Mailbox Settings:

1. Open Account Settings: Follow steps 1-3 from the “Repair Outlook Profile” section to open the Account Settings window in Outlook (File > Info > Account Settings > Account Settings).
2. Select Problematic Account: Select the email account that is experiencing sending issues from the list of accounts.
3. Click “Change”: Click on the “Change…” button above the account list. This will open the “Change Account” window.

4. Verify Account Information: In the “Change Account” window, carefully review the following settings:

   • Your Name: Ensure your name is correctly entered.
   • Email Address: Double-check that your email address is accurate.
   • Account Type: Verify the account type (POP3, IMAP, or Microsoft Exchange).
   • Incoming mail server (POP3 or IMAP server): Confirm the incoming server address is correct for your email provider.
   • Outgoing mail server (SMTP) address: Ensure the outgoing server address is correct for your email provider. This is crucial for sending emails.
   • Username: Verify your username or account name for the email account.
   • Password: Double-check your password. You might consider re-entering it to ensure it’s correct.
   • Remember password: Ensure this box is checked if you want Outlook to remember your password.
   • Require logon using Secure Password Authentication (SPA): Check if your email provider requires SPA. If so, ensure this option is correctly set.

5. Test Account Settings: In the “Change Account” window, click on the “Test Account Settings…” button. Outlook will attempt to send a test email to verify your settings. Check if the test is successful. If it fails, review the error messages for clues about incorrect settings.

6. More Settings: Click on the “More Settings…” button in the “Change Account” window. This opens the “Internet Email Settings” dialog.
7. Outgoing Server Tab: Go to the “Outgoing Server” tab.
   • My outgoing server (SMTP) requires authentication: Ensure this box is checked if your email provider requires SMTP authentication (most providers do).
   • Use same settings as my incoming mail server: Select this option if your outgoing server authentication uses the same credentials as your incoming server. Or, select “Log on using” and provide specific username and password if required by your provider.
8. Advanced Tab: Go to the “Advanced” tab.
   • Incoming server port (POP3 or IMAP): Verify the incoming server port number. Common ports are 995 for POP3 with SSL, 993 for IMAP with SSL, 143 for IMAP without SSL, 110 for POP3 without SSL.
   • Outgoing server (SMTP) port: Verify the outgoing server port number. Common ports are 465 for SMTP with SSL, 587 for SMTP with TLS/STARTTLS, 25 for SMTP without encryption (less common and often blocked).
   • Use the following type of encrypted connection: Check the encryption type for both incoming and outgoing servers. Common options are SSL/TLS or STARTTLS. Choose the appropriate encryption method supported by your email provider.
9. Consult Email Provider Documentation: If you are unsure about the correct settings, refer to your email provider’s help documentation or website for the recommended Outlook settings (server addresses, ports, encryption methods).
10. Apply Changes and Test: After making any necessary corrections, click “OK” in the “Internet Email Settings” window, then click “Next” and “Done” in the “Change Account” window. Restart Outlook and test sending emails again.

Accurate mailbox settings are crucial for Outlook to communicate correctly with your email server.

5. Disable COM Add-ins¶

COM add-ins are third-party plugins that enhance Outlook’s functionality. However, some add-ins can sometimes interfere with Outlook’s operation, potentially causing email sending issues, especially those related to attachments or email processing. To diagnose if an add-in is causing the problem, you can start Outlook in safe mode or disable add-ins one by one.

Steps to Disable COM Add-ins:

Related: loading

A. Start Outlook in Safe Mode (to Test Add-in Interference):

1. Close Outlook: Ensure Outlook is completely closed.
2. Open Run Dialog: Press Windows key + R to open the Run dialog box.
3. Type Safe Mode Command: Type outlook.exe /safe and press Enter. This will launch Outlook in Safe Mode, which disables all add-ins.
4. Test Email Sending in Safe Mode: In Safe Mode, try sending an email (with and without attachments). If emails send successfully in Safe Mode, it strongly suggests that an add-in is the culprit.

B. Disable Add-ins One by One (to Identify Problematic Add-in):

1. Open Outlook (Normal Mode): Launch Outlook in normal mode if you started in Safe Mode for testing.
2. Go to Outlook Options: Click on “File” > “Options.”
3. Select Add-ins: In the Outlook Options window, click on “Add-ins” in the left-hand menu.
4. Manage COM Add-ins: At the bottom of the Add-ins pane, in the “Manage” dropdown, select “COM Add-ins” and click “Go…”.
5. Disable Add-ins: The “COM Add-ins” dialog box will appear, showing a list of installed COM add-ins with checkboxes next to them.
   • Start by Disabling All: Uncheck all the checkboxes to disable all COM add-ins. Click “OK.”
   • Restart Outlook: Restart Outlook for the changes to take effect.
   • Test Email Sending: Try sending emails again. If the issue is resolved, it confirms that an add-in was causing the problem.
   • Re-enable Add-ins One by One (to Isolate Problematic Add-in): If disabling all add-ins fixed the issue, now re-enable them one at a time.
     • Go back to “File” > “Options” > “Add-ins” > “COM Add-ins” > “Go…”.
     • Check the checkbox for one add-in to re-enable it. Click “OK.”
     • Restart Outlook.
     • Test email sending again.
     • Repeat this process, re-enabling one add-in at a time and testing after each re-enablement, until the email sending problem reappears.
     • The add-in that was last re-enabled before the problem returned is likely the problematic one.
6. Remove or Update Problematic Add-in: Once you identify the problematic add-in, you can choose to either:
   • Disable it permanently: Leave its checkbox unchecked in the “COM Add-ins” dialog.
   • Uninstall it: If you don’t need the add-in, you can uninstall it from your computer through “Control Panel” > “Programs and Features” (or “Apps & features” in Windows 10/11).
   • Check for Updates: Visit the add-in vendor’s website to see if there are any updates available for the add-in. An updated version might have bug fixes that resolve the conflict with Outlook.

By systematically disabling and re-enabling add-ins, you can pinpoint if an add-in is causing your email sending issues and take appropriate action.

6. Turn Off Antivirus Email Integration¶

Many antivirus and security software suites include features that integrate with email clients like Outlook to scan incoming and outgoing emails for threats. While this is intended to enhance security, sometimes these email integration features can interfere with email sending, particularly with attachments, or cause delays. Temporarily disabling antivirus email integration can help determine if it’s the source of your sending problems.

Steps to Turn Off Antivirus Email Integration (Temporarily for Testing):

1. Locate Antivirus Software Settings: Open the user interface of your antivirus software. The method to access settings varies depending on the antivirus program you are using (e.g., Norton, McAfee, Avast, Bitdefender, etc.). Look for the antivirus icon in the system tray (bottom right corner of your screen), right-click on it, and look for options like “Open,” “Settings,” “Configuration,” or similar.
2. Find Email Protection or Email Scanning Settings: Within your antivirus software’s settings, look for sections related to “Email Protection,” “Email Scanning,” “Mail Shield,” “Email Security,” or similar terms. The exact naming and location of these settings will depend on your antivirus software.
3. Disable Email Integration/Scanning: Locate the setting that enables email integration or scanning for Outlook (or email clients in general). This might be a checkbox, a toggle switch, or a specific feature you need to disable. Temporarily disable this email integration feature. Do not disable your entire antivirus protection, only the email-specific scanning or integration component.
4. Apply Changes and Restart Outlook: Save the changes you made in your antivirus settings and close the antivirus software’s settings window. Restart Microsoft Outlook.
5. Test Email Sending: Try sending an email with and without attachments in Outlook. Check if the sending issue is resolved after disabling antivirus email integration.
6. Re-enable Antivirus Email Integration (If Issue Resolved): If disabling antivirus email integration resolves the sending problem, it indicates that your antivirus software was likely interfering. You should then re-enable the email integration feature in your antivirus software to maintain email security. However, you might need to configure the antivirus settings further to prevent it from interfering with Outlook in the future. Check your antivirus software’s documentation or support for guidance on configuring email scanning exceptions or settings to work smoothly with Outlook.
7. Consider Antivirus Configuration (If Issue Persists): If disabling email integration did not resolve the issue, you can re-enable it. The problem is likely not related to antivirus interference in this case.

Disabling antivirus email integration is primarily a diagnostic step. If it resolves the problem, it points to a conflict that needs to be addressed either by adjusting antivirus settings or potentially switching to a different antivirus solution if the interference is persistent and unconfigurable.

7. Zip Files Before Sending Large Attachments¶

If you are having trouble sending emails with large attachments, especially if you suspect the file size is near the limit, compressing the files into a ZIP archive before attaching them to Outlook can be a practical workaround. Zipping files reduces their file size, often significantly, making them easier to send via email. Windows has built-in ZIP archive functionality, making this a quick and convenient method.

Steps to Zip Files Before Attaching to Outlook:

1. Locate Files or Folders: Identify the file(s) or folder(s) you want to attach to your email in Outlook.
2. Select Files/Folders: Select the files or folders you want to zip. You can select multiple files by holding down the Ctrl key while clicking on each file or folder.
3. Right-Click and “Send to”: Right-click on the selected files or folders. In the context menu that appears, hover over “Send to.”
4. Choose “Compressed (zipped) folder”: In the “Send to” submenu, click on “Compressed (zipped) folder.”
5. Windows Creates ZIP File: Windows will create a new ZIP archive file in the same location as the original files or folders. The ZIP file will have the same name as the selected item (or the first selected item if you selected multiple items), with a .zip extension.
6. Attach ZIP File to Outlook Email: In Outlook, compose your email as usual. When you are ready to attach the file, click on the “Attach File” option.
7. Browse and Select ZIP File: In the file explorer window that opens, navigate to the location where the ZIP file was created. Select the ZIP file and click “Insert” or “Attach.”
8. Send Email: Complete your email and click “Send.” Outlook will now attach the compressed ZIP file to your email, which should be smaller in size than the original files.

Zipping is especially useful for sending multiple files or folders as a single attachment and for reducing the size of large files like images, documents, or presentations to fit within email attachment size limits.

8. Check for Blocked File Types¶

Outlook, for security reasons, blocks certain file types from being sent or received as attachments. These blocked file types are typically those that are considered potentially harmful or executable, such as .exe, .bat, .vbs, .js, and others. If you are trying to send an attachment with a blocked file extension, Outlook will prevent you from sending the email or the recipient might not receive the attachment.

Steps to Check for and Handle Blocked File Types:

1. Identify Attachment File Type: Determine the file extension of the attachment you are trying to send (e.g., .exe, .zip, .doc, .pdf, etc.).
2. Check if File Type is Blocked (General List): Be aware that Outlook commonly blocks executable files and script files. Some common blocked extensions include: .exe, .com, .bat, .cmd, .vbs, .js, .lnk, .pif, .scr, and more. The exact list can vary slightly depending on Outlook versions and security settings.
3. Rename File Extension (Use with Caution and at Recipient’s Request): As a very last resort and only if you are absolutely certain the file is safe and the recipient is expecting it and knows how to handle it: you can try renaming the file extension to something less likely to be blocked, such as changing .exe to .exe.txt. However, this is strongly discouraged for executable files and potentially harmful file types. It’s generally better to avoid sending blocked file types via email directly due to security risks.
4. Use File Archiving (ZIP or Similar): A safer and more common approach is to archive the blocked file type into a ZIP archive (as described in step 7). ZIP files are generally not blocked by default (though they could be in very strict security environments). Zipping can sometimes bypass file type blocking, but it’s not guaranteed in all cases.
5. Use Cloud Storage and Share Links: The most secure and recommended method for sharing files that might be blocked or are large is to use cloud storage services like OneDrive, Google Drive, Dropbox, or similar.
   • Upload File to Cloud Storage: Upload the file to your cloud storage account.
   • Generate Shareable Link: Create a shareable link for the uploaded file. Most cloud services allow you to create links with different permission levels (view-only, edit, etc.).
   • Send Link in Email: Instead of attaching the file directly to your Outlook email, paste the shareable link into the email body. The recipient can then click on the link to download the file from the cloud storage.

Using cloud storage links is a secure and reliable way to share files that might be blocked by email systems or are too large to send as attachments. It also provides better control over file access and versioning.

By following these troubleshooting steps, you should be able to identify and resolve most common email sending issues in Outlook on Windows. Remember to test after each step to see if the problem is fixed. If you continue to experience problems, providing detailed information about any error messages or specific scenarios you encounter when seeking further support will be helpful.

If you found these troubleshooting steps helpful, or if you have any further questions or additional tips, please feel free to leave a comment below!