How to Fix Outlook Emails Remaining in the Outbox and Failing to Send in Microsoft 365

Summary

This guide helps you troubleshoot and resolve: How to Fix Outlook Emails Remaining in the Outbox and Failing to Send in Microsoft 365. Follow the steps below to fix the issue.

Common Causes

If your emails are sitting in the Outbox and refusing to send in Microsoft 365 Outlook, the issue is usually caused by a connection problem, an oversized attachment, or a corrupted local data file. This guide provides steps for Brisbane small business users to clear the Outbox and restore normal email flow.

Quick Fix Steps

1. Check your internet connection to ensure you are online.
2. Restart Outlook to force a fresh connection to the Microsoft 365 servers.
3. Open the Send/Receive tab and select Send All.
4. Check the Outbox for emails with large attachments and delete or reduce them.

Detailed Instructions

1. Work Offline and Clear the Outbox

If an email is stuck, Outlook may keep attempting to send it, blocking other messages. Working offline stops this process so you can edit or delete the stuck email.

1. In Outlook, go to the Send/Receive tab on the ribbon.
2. Click the Work Offline button. The status bar at the bottom of the window will now show Working Offline.
3. Navigate to the Outbox folder in your folder pane.
4. Right-click the email that is stuck and select Delete, or open it to remove large attachments and try sending again.
5. Once the Outbox is empty, click Work Offline again to reconnect.

2. Check for Large Attachments

Microsoft 365 has a limit on the size of emails you can send. If an attachment is too large, the message will remain in the Outbox indefinitely.

• If the email contains a large file, remove the attachment and upload the file to OneDrive or SharePoint.
• Share a link to the file in the email instead of attaching the document directly.

3. Repair the Outlook Data File

A corrupted Offline Outlook Data File (.ost) can prevent messages from leaving the Outbox.

1. Close Outlook completely.
2. Open the Control Panel and search for Mail.
3. Click Email Accounts, then select the Data Files tab.
4. Select your data file and click Open File Location.
5. Close the window and run the SCANPST.EXE tool (Inbox Repair Tool) located in your Office installation folder to analyse and repair the file.

Troubleshooting

Outlook is stuck in "Disconnected" mode

If the status bar shows Disconnected, Outlook cannot communicate with the Microsoft 365 servers.

1. Restart your router and computer.
2. Check if you can browse other websites to confirm your internet is working.
3. Ensure your VPN is not blocking Outlook traffic.

Emails send on the web but not in Outlook

Log into Outlook on the web. If you can send emails there, the issue is local to your Outlook installation.

1. Go to File > Office Account > Update Options > Update Now.
2. If updates do not fix the issue, create a new Outlook profile via the Control Panel Mail settings.

If you have followed these steps and your emails are still stuck in the Outbox, please Open a Ticket with our Brisbane support team.

Related Articles:

• Setting Up an Email Account in Outlook (POP/IMAP/Exchange)
• Managing Email Signatures in Outlook
• Troubleshooting Outlook Send/Receive Errors
• Backing Up and Restoring Outlook Data Files (.pst/.ost)
• Organizing Emails with Rules and Alerts in Outlook
• Using Outlook Calendar and Scheduling Meetings

Still Having Issues?