Outlook Not Sending Emails? Here’s Why and How to Fix It

When Outlook not sending emails occurs and messages remain stuck in the Outbox folder, it can bring your workflow to a complete halt. This is one of the most frustrating issues Microsoft Outlook users encounter, whether you’re using Outlook for Microsoft 365, Outlook 2024, or the classic desktop application. Emails can get trapped in the Outbox for various reasons—from oversized attachments and network disconnections to corrupted profiles and incorrect server settings.

If you’re dealing with email sending issues, check out our Gmail not sending emails guide and explore our Windows 11 troubleshooting hub for more solutions.

Why Is Outlook Not Sending Emails? (Root Causes)

Understanding why Outlook not sending emails happens is the first step toward a permanent fix. Here are the most common causes:

• Large attachments: When an email contains an attachment exceeding your provider’s size limit (typically 25 MB for Outlook.com or 150 MB for Exchange Online), it gets stuck in the Outbox.
• Offline mode: If Outlook is in “Work Offline” mode, it queues emails instead of sending them until you reconnect.
• Network connectivity issues: Unstable internet connections or server timeouts prevent emails from leaving the Outbox.
• Corrupted add-ins: Third-party add-ins can interfere with Outlook’s sending functionality.
• Incorrect SMTP settings: Wrong outgoing mail server settings block email transmission.
• Corrupted Outlook profile: A damaged user profile can cause various issues, including sending failures.
• Firewall or antivirus interference: Security software may block Outlook’s outgoing connections.
• Full mailbox storage: When your mailbox or cloud storage is full, sending can be blocked.
• Stuck read receipts: Sometimes a read receipt request can get stuck and block the queue.
• Delayed delivery settings: If “Delay Delivery” is enabled, the email won’t send until the scheduled time.

Now let’s explore the most effective methods to fix Outlook not sending emails.

Method 1: Check If Outlook Is in Offline Mode

One of the most common reasons for Outlook not sending emails is that the application is in “Work Offline” mode. When Outlook is offline, it queues emails in the Outbox instead of sending them to the mail server.

For Classic Outlook (Microsoft 365 / Office 2024):

1. Open Outlook and go to the Send/Receive tab at the top.
2. Look for the Work Offline button in the Preferences section.
3. If the button is highlighted (blue or gray), click it to turn off offline mode.
4. The status bar at the bottom of the Outlook window should now show “Connected” or “Online”.
5. Click Send/Receive All Folders or press F9 to manually trigger a send attempt.

For New Outlook (Windows 11 app):

1. Click the Settings gear icon in the top-right corner.
2. Go to View all Outlook settings → Mail → Sync email.
3. Confirm the account is showing as “Connected”.
4. If prompted, sign in again to refresh your credentials.

If the status bar shows “Trying to connect” or “Disconnected,” verify your internet connection by opening a website in your browser.

Method 2: Remove or Reduce Large Attachments

When Outlook not sending emails is the issue, large attachments are often the primary culprit. Most email providers enforce strict size limits—Outlook.com limits emails to 25 MB total (body + attachments), while Exchange Online allows up to 150 MB.

1. Go to the Outbox folder in the left navigation pane.
2. Double-click the stuck email to open it in a separate window.
3. If the email has a large attachment, right-click it and select Remove.
4. Alternatively, drag the message from Outbox to Drafts, open it, remove the attachment, and try sending again.
5. If you must send the file, upload it to OneDrive or Google Drive and insert a sharing link instead.
6. After removing the attachment, click Send again.

Tip: If the email won’t let you delete or move it because Outlook is “trying to transmit,” close Outlook completely first, then reopen it and try again.

Method 3: Restart Outlook Completely

Sometimes a simple restart can resolve Outlook not sending emails. However, simply closing the Outlook window may not fully shut down the application process.

1. Close Outlook completely—make sure it’s not running in the background.
2. Press Ctrl + Alt + Delete and select Task Manager.
3. Go to the Processes tab and look for outlook.exe.
4. If it appears, select it and click End Process or End Task.
5. Wait a few seconds, then reopen Outlook.
6. Check if the emails in Outbox are now sending automatically.
7. If they’re still stuck, try moving them to Drafts and sending again.

This method works because it clears any temporary locks or sync conflicts that may have been preventing the send process. When Outlook not sending emails persists after a normal restart, this forced termination approach often resolves the issue.

Method 4: Start Outlook in Safe Mode

If Outlook not sending emails persists, a problematic add-in might be the cause. Starting Outlook in Safe Mode disables all add-ins, allowing you to test if they’re interfering with the send process.

1. Press Windows + R to open the Run dialog box.
2. Type outlook.exe /safe and press Enter.
3. Outlook will open with all add-ins disabled.
4. Try sending a test email.
5. If it works in Safe Mode: An add-in is causing Outlook not sending emails.
6. Go to File → Options → Add-ins.
7. At the bottom, select COM Add-ins from the Manage dropdown and click Go.
8. Disable all add-ins, then re-enable them one by one to find the culprit.
9. If it doesn’t work in Safe Mode: The issue is deeper—proceed to the next methods.

Some users have reported that automatically added Outlook add-ins from Microsoft can cause sending issues. Disabling unnecessary add-ins can resolve Outlook not sending emails effectively.

Method 5: Verify SMTP Server Settings

Incorrect outgoing mail server (SMTP) settings are another common reason for Outlook not sending emails. This is especially true for third-party email accounts like Gmail, Yahoo, or custom domain emails.

1. In Outlook, go to File → Account Settings → Account Settings again.
2. Select your email account and click Change.
3. Click More Settings → Outgoing Server tab.
4. Ensure “My outgoing server (SMTP) requires authentication” is checked.
5. Go to the Advanced tab and verify the following settings:

6. Click OK and then Next to test the settings.
7. If the test fails, double-check your credentials and server settings with your email provider.

For official guidance on resolving Outlook not sending emails, visit Microsoft’s official support page for sending issues.

Method 6: Repair Office Installation

Corrupted Office installation files can cause Outlook not sending emails. Repairing the installation can fix these issues without affecting your personal data.

1. Close all Office applications, including Outlook.
2. Open Settings (Windows + I) → Apps → Installed apps (or Apps & features).
3. Find Microsoft 365 or Microsoft Office in the list.
4. Click the three dots (⋮) and select Modify.
5. Choose Quick Repair first—this is faster and doesn’t require an internet connection.
6. If Outlook not sending emails persists, run Online Repair—this takes longer but performs a more thorough fix.
7. Follow the on-screen instructions and restart your computer when complete.
8. Open Outlook and test if emails are now sending.

For users with the Outlook app from the Microsoft Store (New Outlook), you can also try resetting the app: go to Settings → Apps → Installed apps, find Outlook, click Advanced Options, and select Repair or Reset.

Method 7: Create a New Outlook Profile

A corrupted Outlook profile is a frequent cause of Outlook not sending emails and other persistent issues. Creating a new profile can resolve these problems without losing your data.

1. Close Outlook completely.
2. Open the Control Panel (search for it in the Start menu).
3. Change the view to Large icons or Small icons.
4. Click on Mail (Microsoft Outlook).
5. In the Mail Setup dialog, click Show Profiles.
6. Click Add to create a new profile.
7. Give it a name (e.g., “Outlook-New”) and click OK.
8. Follow the prompts to set up your email account in the new profile.
9. Under “Always use this profile,” select the new profile from the dropdown.
10. Click OK and restart Outlook.
11. Test if emails are now sending correctly.

If the new profile works, you can gradually migrate your data (emails, contacts, calendar) from the old profile. Your PST/OST files remain intact, so you won’t lose any data when fixing Outlook not sending emails.

Method 8: Check Firewall and Antivirus Settings

Security software can sometimes block Outlook’s ability to connect to the outgoing mail server, resulting in Outlook not sending emails.

1. Temporarily disable your antivirus or firewall to test if it’s causing the issue.
2. If emails send after disabling, add Outlook as an exception in your security software.
3. For Windows Firewall:
   • Go to Control Panel → Windows Defender Firewall.
   • Click Allow an app or feature through Windows Defender Firewall.
   • Find Microsoft Outlook in the list and ensure both Private and Public boxes are checked.
   • If it’s not listed, click Allow another app and browse to C:\Program Files\Microsoft Office\root\Office16\OUTLOOK.EXE.
4. For third-party antivirus: Look for email scanning or firewall settings and add Outlook to the exception list.
5. After making changes, restart Outlook and test sending.

For the New Outlook (Microsoft Store app), you may need to allow it through the firewall separately. The executable is typically located in the WindowsApps folder.

Advanced Troubleshooting for Outlook Not Sending Emails

If the methods above haven’t resolved Outlook not sending emails, try these advanced solutions:

Clear Offline Items in Outbox

Right-click the Outbox folder and select Clear Offline Items. Then force a Send/Receive by pressing F9.

Disable Cached Exchange Mode

Go to File → Account Settings → Account Settings → select your account → Change → More Settings → Advanced tab. Uncheck “Use Cached Exchange Mode”, restart Outlook, and test. This can help when Outlook not sending emails is related to synchronization issues.

Check for Stuck Read Receipts

Sometimes a read receipt request can get stuck and block the queue. Go to Sent Items, find any emails with pending read receipts, and delete or archive them.

Check Delayed Delivery Settings

Open the stuck email, go to the Options tab, and ensure “Delay Delivery” is not enabled. This setting can cause Outlook not sending emails until the scheduled time.

Use Microsoft Support and Recovery Assistant

Download and run the Microsoft Support and Recovery Assistant (SaRA). This official tool can automatically diagnose and fix Outlook not sending emails.

Check Mailbox Storage

If your mailbox is full, you won’t be able to send or receive emails. Check your mailbox storage and free up space by deleting old emails or emptying the Deleted Items folder.

Check for Service Outages

Visit DownDetector’s Outlook status page to check if Microsoft 365 or Outlook is experiencing a service outage that could cause Outlook not sending emails.

Conclusion

When Outlook not sending emails and they remain stuck in the Outbox, the issue can usually be resolved by following the methods outlined above. Start with the simplest solutions—checking offline status and removing large attachments—then progress to more advanced fixes like repairing Office or creating a new profile. Most cases of Outlook not sending emails are caused by large attachments, offline mode, or network connectivity issues, which are all relatively easy to fix.

If you’ve tried all these methods and Outlook not sending emails persists, consider contacting your IT administrator (for business accounts) or Microsoft Support for further assistance. Remember to always keep your Outlook and Windows updated to prevent future issues.

For more Windows 11 troubleshooting guides, explore our Windows 11 troubleshooting hub.

Related Guides

• Gmail Not Sending Emails? Fix Stuck in Outbox
• Windows 11 Sound Not Working? Fix It Fast
• Windows 11 Start Menu Not Working? Try These Fixes
• Windows 11 High CPU Usage? Complete Fix Guide
• Windows 11 File Explorer Not Responding? 9 Ways to Fix
• Windows 11 Update Stuck? How to Fix It
• Windows 11 Bluetooth Not Working? Fix Guide

Frequently Asked Questions

Why are my emails stuck in the Outbox and not sending in Outlook?

Emails get stuck in the Outbox when Outlook not sending emails occurs due to large attachments, offline mode, network issues, incorrect SMTP settings, or corrupted add-ins. The most common cause is an attachment that exceeds your email provider’s size limit.

How do I force Outlook to send emails stuck in Outbox?

To force Outlook to send stuck emails, first check that you’re not in offline mode (Send/Receive → Work Offline should be unselected). Then press F9 to manually trigger a Send/Receive. If that doesn’t work, restart Outlook completely using Task Manager to end the outlook.exe process, then reopen and try again to resolve Outlook not sending emails.

What is the maximum attachment size for Outlook?

For Outlook.com accounts, the maximum email size (including attachments) is 25 MB. For Exchange Online (Microsoft 365 business), the limit is 150 MB. If your attachment exceeds these limits, Outlook not sending emails will occur and the message will remain in the Outbox.

Will reinstalling Outlook fix emails stuck in Outbox?

Reinstalling Outlook may help if the issue is caused by corrupted installation files. However, before reinstalling, try running a Quick Repair or Online Repair from the Office installation settings. These options often fix Outlook not sending emails without requiring a full reinstall.

Can a full mailbox cause Outlook not sending emails?

Yes, if your mailbox or OneDrive storage is full, you won’t be able to send or receive emails. Check your mailbox storage status and free up space by deleting old emails, emptying the Deleted Items folder, or archiving older messages to fix Outlook not sending emails.

How do I check my SMTP settings in Outlook?

Go to File → Account Settings → Account Settings, select your email account, click Change, then More Settings, and go to the Outgoing Server and Advanced tabs. Verify that your SMTP server, port, and encryption settings match your email provider’s requirements to resolve Outlook not sending emails.

Why does Outlook say “Trying to connect” and not send emails?

When Outlook shows “Trying to connect” and Outlook not sending emails occurs, it usually indicates network issues, server problems, or firewall interference. Check your internet connection, verify that Outlook isn’t in offline mode, and temporarily disable your firewall or antivirus to test if they’re blocking the connection.

Does creating a new Outlook profile delete my emails?

No, creating a new Outlook profile does not delete your emails, contacts, or calendar items. Your data is stored in PST or OST files that remain on your computer. Creating a new profile simply creates a new set of settings and configurations to fix Outlook not sending emails.

How do I clear the Outbox in Outlook?

To clear the Outbox, open the Outbox folder, select all emails, and either delete them or move them to Drafts. If you can’t delete them because Outlook is trying to send, restart Outlook first, then clear the Outbox. This can help when Outlook not sending emails is caused by a stuck message.