How to Fix Outlook Email Attachments Not Sending or Receiving in Microsoft 365

Summary

This guide helps you troubleshoot and resolve: How to Fix Outlook Email Attachments Not Sending or Receiving in Microsoft 365. Follow the steps below to fix the issue.

Common Causes

Outlook attachment issues usually stem from file size limits, connectivity problems, or conflicts with add-ins and security software. This guide covers the most effective fixes for Microsoft 365 Outlook on Windows, Mac, and the web.

Quick Fix Steps

1. Check your internet connection and restart Outlook.
2. Verify the attachment size does not exceed 25 MB.
3. Open Outlook in safe mode to rule out add-in conflicts.
4. Clear the Outbox if messages are stuck.
5. Test using Outlook on the web at outlook.office.com.

Detailed Instructions

Check Attachment Size

Microsoft 365 typically limits email attachments to 25 MB per message. If your file is larger, use OneDrive or SharePoint to share a link instead of attaching the file directly.

Start Outlook in Safe Mode (Windows)

Safe mode disables third-party add-ins that can block attachments from sending or receiving.

1. Close Outlook completely.
2. Press Windows Key + R to open the Run dialog.
3. Type outlook.exe /safe and press Enter.
4. Select your profile when prompted and click OK.
5. Try sending or receiving an email with an attachment.

If attachments work in safe mode, an add-in is likely causing the issue. Go to File > Options > Add-ins, select COM Add-ins from the dropdown, click Go, and clear the checkboxes to disable add-ins one by one.

Start Outlook in Safe Mode (Mac)

1. Close Outlook completely.
2. Hold the Option key and click the Outlook icon in the Dock to launch.
3. Select your profile when prompted and click Continue.
4. Try sending or receiving an email with an attachment.

Clear Stuck Messages from the Outbox

Emails with large attachments can get stuck in the Outbox and block new messages from sending.

1. Go to the Send/Receive tab and click Work Offline.
2. Open the Outbox folder.
3. Right-click the stuck message and select Delete, or open it and remove the attachment.
4. Click Work Offline again to reconnect.
5. Click Send/Receive All Folders.

Repair Outlook Data Files (Windows)

A corrupted Outlook data file can prevent attachments from downloading correctly. Note: SCANPST.EXE repairs .pst files. For Microsoft 365 accounts using .ost files, the .ost file will typically rebuild automatically when the account is reconnected.

1. Close Outlook.
2. Open the Control Panel and go to Mail (or Microsoft Outlook).
3. Click Data Files, select your account, and note the file path.
4. Close the dialogs and open File Explorer to that location.
5. Run the Inbox Repair tool (SCANPST.EXE) against the .pst file.
6. Follow the prompts to repair any errors found.

Check Outlook on the Web

If attachments fail in the desktop app but work in a browser, the issue is likely local to your Outlook installation rather than your mailbox.

1. Go to outlook.office.com and sign in.
2. Compose a new message and attach a small file.
3. Send the message to yourself and verify the attachment arrives.

Troubleshooting

Attachment Does Not Appear in Received Email

• Ask the sender to resend the file using a cloud-sharing link if it exceeds 25 MB.
• Check your Junk Email folder; some attachments are filtered automatically.
• Ensure your antivirus software is not stripping attachments from incoming mail.
• Clear the Outlook cache by deleting files in %localappdata%\Microsoft\Outlook\RoamCache.

Emails Stay in the Outbox

• Confirm you are connected to the internet and not in Work Offline mode.
• Reduce the attachment size and try again.
• Check that your Microsoft 365 subscription is active and licenced.

Note: If you regularly need to send large files, consider using OneDrive or SharePoint. Upload the file, copy the sharing link, and paste it into your email instead of attaching the file directly.

Warning: Do not delete Outlook data files without first confirming you have a backup. Removing a .pst or .ost file can result in permanent loss of emails, contacts, and calendar items stored locally.

If you have completed these steps and attachments still fail to send or receive, Open a Ticket with 220 Internet Services support.

For general mail flow problems, see our guide on Email not sending or receiving.

Still Having Issues?