Outlook not Attaching Files: 5 Ways to Permanently Fix It

If Outlook is not attaching files, it usually means the program is hitting size limits, blocking certain file types, or running into profile, add-in, or cache problems. This guide explains why it happens and how to fix it quickly.

Why Outlook Is Not Attaching Files

Outlook may refuse attachments if the file is too large (over 20–25 MB). Certain file types like .exe, .bat, or .js are also blocked for security. Add-ins or a corrupted Outlook profile can interfere with attachments, while weak internet or a nearly full mailbox may cause failures. Sometimes antivirus software blocks outgoing files, or corrupted cache and temporary folders disrupt the process.

What can I do if Outlook is not attaching files?

1. Compress files for attaching into a ZIP Archive

1. Press the Windows key + E to access File Explorer.
   

   

2. Open a directory that includes the files you can’t attach to an Outlook email.
3. Hold the Ctrl key to select all files to include in your attachment.
4. Right-click and select Compress to ZIP file.
   

   

5. Enter a title for your ZIP.
6. Then try attaching the ZIP archive to an Outlook email.

2. Disable compatibility mode for Outlook

1. Right-click an Outlook shortcut icon or its EXE application file to select Properties. 
2. Select Compatibility on Outlook’s Properties window. 
3. Uncheck the Run this program in compatibility mode box if that setting is selected.

   

4. Press Apply and OK to save the reconfigured settings. 
   

   

NOTE

This resolution is recommended if you see an Operation failed message when trying to attach files to Outlook emails.

3. Change the email message’s format

1. Click Outlook’s File tab.
2. Select Options to bring up a Settings window.
3. Click the Mail tab.
4. Select HTML or Plain Text in the compose format drop-down menu if Outlook is set to Rich Text.
   

   

5. Press the Outlook Options window’s OK button.

4. Run Outlook in its Safe Mode

1. Bring up Windows 11’s Run command dialog by clicking Start with the right mouse button and selecting that accessory on the Win + X menu.
   

   

2. Input this Safe Mode command: Outlook.exe /safe
3. Click OK to launch Outlook in Safe Mode.
   

   

4. Try attaching attachments to an email again.

5. Disable Outlook add-ins

1. Open Outlook, and click its File tab.
2. Click Options on the File tab.
3. Select the Add-ins tab.
   

   

4. Then click COM Add-on on the Manage drop-down menu.
5. Press the Go button.
6. Uncheck the checkboxes for enabled Outlook add-ins.
   

   

7. Select OK on the COM Add-ins window.

What is the maximum attachment size in Outlook 365?

The maximum attachment size for Outlook 2019 and 2016 is 20 megabytes. That limit applies to single or multiple files irrespective of the email server.

So, check if files for an attachment eclipse the 20-megabyte mark before you try to attach them to an Outlook email. If they do, try compressing the files in an archive as outlined for solution one.

However, that 20 megabyte doesn’t apply to users with Exchange Server accounts. Instead, Outlook applies an Exchange server limit. You can change that limit in the Exchange Management Console.

Those are some more probable potential fixes for Outlook not attaching files. Updating Outlook, disabling third-party antivirus software, and repairing that app’s PST data file are other potential resolutions worth trying.

Also, here’s what to do if Outlook 2016 crashes when opening an email with attachment. It’s time to verify your antivirus, install the latest updates, or apply our other tips.

Have you fixed Outlook not attaching files with a resolution not specified above? If so, feel free to share your solution for that issue in the comments section below.