Outlook Email Stuck in Outbox With Large Attachment: How to Cancel or Resize

An email with a large attachment can get stuck in your Outlook Outbox. This happens when the message size exceeds your mail server’s sending limit. The email will not send and cannot be deleted normally. This article explains how to cancel the stuck message and how to resize the attachment to send it successfully.

Why Large Attachments Get Stuck in the Outbox

Outlook tries to send messages immediately when you click Send. If an email with a large attachment exceeds your mail provider’s size limit, the server rejects it. Outlook will keep retrying to send it, locking the message in the Outbox. Common limits are 10 MB for older servers and 20 MB or 25 MB for Microsoft 365. Network interruptions or a slow connection can also cause timeouts during the upload of a large file, resulting in the same stuck state. The message becomes read-only while sending is attempted, which is why you cannot delete it using the Delete key.

Steps to Cancel the Stuck Email

You must first stop Outlook’s send/receive process to unlock the message. The most reliable method is to use Work Offline mode.

1. Enable Work Offline mode
   Go to the Send / Receive tab on the ribbon. Click the Work Offline button. The button will highlight in orange, confirming Outlook is no longer trying to connect to your mail server.
2. Delete the stuck message
   Navigate to your Outbox folder. Select the email that is stuck. Press the Delete key on your keyboard. The message should move to the Deleted Items folder without error.
3. Disable Work Offline and empty Deleted Items
   Click the Work Offline button again to turn it off. Finally, right-click your Deleted Items folder and select Empty Folder to permanently remove the cancelled message.

Alternative Method: Force a Send Failure

If Work Offline does not work, you can force the send operation to fail by reducing the server timeout. This unlocks the message.

1. Open Advanced Account Settings
   Go to File > Account Settings > Account Settings. Select your email account and click Change. In the dialog box, click More Settings.
2. Adjust the server timeout
   Go to the Advanced tab. Find the Server Timeouts slider. Drag it all the way to the left to the shortest setting, usually 1 minute. Click OK.
3. Trigger a send and delete the message
   Click Next, then Finish, and close the Account Settings window. Outlook will attempt to send the message again, but it will fail quickly due to the short timeout. After the error appears, you can now delete the email from the Outbox. Remember to go back and reset your Server Timeouts to a normal value.

How to Resize and Resend a Large Attachment

After cancelling the stuck email, you need to reduce the file size to send it. The best practice is to avoid attaching large files directly.

Method 1: Share a Link from OneDrive or SharePoint

1. Upload your file to the cloud
   Save the large file to your OneDrive or your organization’s SharePoint site. Ensure the upload is complete.
2. Get a shareable link
   Right-click the file in OneDrive File Explorer or SharePoint. Select the Share option. Choose Anyone with the link or Specific people, then click Copy link.
3. Paste the link in a new email
   Create a new email in Outlook. Paste the copied link into the message body. Add a brief explanation. The recipient can download the file without size restrictions.

Method 2: Compress the File Before Attaching

1. Use file compression
   Right-click the file or folder in Windows File Explorer. Select Send to, then Compressed (zipped) folder. This creates a new .zip file which is often smaller.
2. Check the new file size
   Right-click the new .zip file and select Properties. Check the Size to ensure it is under your email server’s limit, typically under 20 MB.
3. Attach the compressed file and send
   Create a new email and attach the .zip file. Click Send. The message should leave the Outbox normally.

If the Email Remains Stuck After These Steps

Outbox folder shows error but won’t delete

Try closing Outlook completely. Open the Windows Task Manager with Ctrl+Shift+Esc. Look for any Outlook processes under the Details tab and end them all. Restart Outlook and immediately go to Work Offline mode before it attempts to send. Then delete the message.

Outlook crashes when opening the Outbox

A corrupted Outlook data file can cause this. Start Outlook in safe mode by pressing Win+R, typing outlook.exe /safe, and pressing Enter. In safe mode, navigate to the Outbox and delete the problem message. If successful, exit and restart Outlook normally.

Large attachment is a video or image file

Media files are often too large to compress effectively. Use a dedicated video compression tool or reduce the image resolution before attaching. For frequent sending of media, a cloud sharing service is the only practical solution.

Direct Attachment vs Cloud Link: Comparison

Item	Direct File Attachment	OneDrive/SharePoint Link
Server Size Limit	Subject to limit (e.g., 20MB)	Bypasses limit
Outbox Stuck Risk	High for files over 10MB	None
Recipient Action	Open or save attachment	Click link to download
File Version Control	Static copy in email	Always accesses latest cloud version
Your Storage Impact	Uses email quota	Uses OneDrive/SharePoint storage

You can now remove a stuck email from your Outbox and choose a better method for sending large files. Use Work Offline mode as your first step to cancel any pending send operation. For future sends, get into the habit of sharing cloud links instead of attaching large files directly. An advanced tip is to set an Outlook rule that warns you if an outgoing message exceeds 15 MB, giving you a chance to fix it before it gets stuck.