How to Fix Outlook 'Cannot Send This Item' Error When Sending Large Attachments in Microsoft 365

Summary

This guide helps you troubleshoot and resolve: How to Fix Outlook 'Cannot Send This Item' Error When Sending Large Attachments in Microsoft 365. Follow the steps below to fix the issue.

Common Causes

Microsoft 365 Outlook has strict limits on the size of email attachments. When you try to send a message with a file that exceeds these limits, you may see an error stating that Outlook cannot send the item. This is a common issue for small businesses sharing large documents, high-resolution images, or project files. This guide explains how to resolve the error by reducing attachment sizes, using OneDrive sharing links, or adjusting Outlook settings.

Quick Fix Steps

1. Reduce the attachment size or remove unnecessary files from the email.
2. Upload large files to OneDrive and share a link instead of attaching the file.
3. Restart Outlook and attempt to send the email again.
4. Check your internet connection and ensure you are not in Offline mode.

Detailed Instructions

Method 1: Share Files Using OneDrive

Using OneDrive is the recommended method for sending large files. It bypasses Outlook attachment limits and allows recipients to download the file directly from the cloud.

1. Open File Explorer and locate the file you want to send.
2. Right-click the file and select Share, or upload it to your OneDrive folder via OneDrive Web.
3. In the sharing dialog, select Copy link to generate a shareable URL.
4. Open Outlook and create a new email message.
5. Paste the copied link into the body of the email.
6. Add a brief note explaining that the recipient can download the file using the link.
7. Send the email as normal.

Method 2: Compress Large Attachments

If you prefer to attach the file directly, compressing it may reduce the size enough to fall within Outlook's limits.

1. Right-click the file or folder you wish to send.
2. Select Send to > Compressed (zipped) folder.
3. Attach the newly created .zip file to your Outlook email.
4. Attempt to send the message.

Method 3: Check Outlook Offline Mode and Connection

Sometimes send errors occur because Outlook is disconnected from the mail server.

1. Look at the bottom of the Outlook window for the status indicator.
2. If you see Working Offline, go to the Send/Receive tab on the ribbon.
3. Click the Work Offline button to toggle it off and reconnect.
4. Wait for Outlook to synchronise, then try sending the email again.

Troubleshooting

Attachment Still Fails to Send

If the error persists after trying the methods above, the attachment may still exceed the server-side limit imposed by Microsoft 365 or your email provider.

• Verify the file size is under 20 MB. Most Microsoft 365 environments block attachments larger than this threshold.
• Try sending the email to yourself first to confirm whether the issue is with your account or the recipient's mail server.
• Clear the Outlook cache by closing Outlook, pressing Windows Key + R, typing %localappdata%\Microsoft\Outlook, and deleting the contents of the RoamCache folder.

Error Occurs on All Emails

If you cannot send any emails, even without attachments, the issue may be related to your account configuration or send/receive settings.

• Review our guide on Troubleshooting Outlook Send/Receive Errors.
• Ensure your email account is correctly configured by following Setting Up an Email Account in Outlook.
• Check for large items stuck in your Outbox folder and delete or move them to Drafts.

If you continue to experience issues sending emails with attachments, please Open a Ticket with our Brisbane support team for further assistance.

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