You cannot send an email because Outlook blocks attachments over 20 MB. This limit is set by your email provider, not the Outlook application itself. Most corporate and consumer email servers enforce this restriction to manage network traffic and storage. This article explains the technical cause and provides several reliable methods to send large files.
Key Takeaways: Sending Files Larger Than 20 MB
- OneDrive or SharePoint Link: Upload the file to cloud storage and share a link instead of attaching the file directly.
- File > Info > Compress Media: Reduces the size of video and image files directly within Outlook before attaching.
- Archive (ZIP) the File: Use Windows File Explorer to compress the file, which can sometimes reduce its size below the limit.
Why Email Servers Block Large Attachments
The 20 MB attachment limit is a common configuration for Microsoft Exchange Server and other email services. This policy prevents large files from clogging mail queues, exceeding mailbox quotas, and consuming excessive bandwidth. When you attempt to send a file larger than this limit, Outlook will display an error and prevent the email from being sent. The limit is applied by the server when it receives your outgoing message, which is why the error may appear after you click Send.
It is important to know that this is a server-side restriction. Changing settings within the Outlook desktop application will not increase this limit. Your organization’s IT administrator controls the maximum send and receive size, which can be different. Some providers may allow receiving larger files than you can send.
Methods to Send Large Files from Outlook
Since you cannot change the server limit, you must use alternative methods to transfer the file. The most effective approach is to avoid attaching the file to the email entirely.
Share a Link from OneDrive or SharePoint
This is the recommended method for Microsoft 365 users. You upload the file to a cloud service and insert a permission-controlled link into your email.
- Upload your file to OneDrive
Open your OneDrive folder in File Explorer and drag the large file into it. Wait for the sync icon to show the upload is complete. - Get a shareable link in Outlook
In a new email, go to the Insert tab. Click Attach File, then browse cloud locations. Select your file from OneDrive. Outlook will attach it as a cloud link by default. - Set link permissions
After inserting, click the attached link in the email body. A menu appears letting you change permissions, like allowing recipients to view or edit the file.
Compress the File Before Attaching
For files slightly over the limit, compression can help. This works best for documents, spreadsheets, and text-based files.
- Create a ZIP file in Windows
Right-click the file or folder in File Explorer. Select Send to, then choose Compressed (zipped) folder. A new .zip file will be created. - Check the new file size
Right-click the ZIP file, select Properties, and check its Size. If it is under 20 MB, you can attach it to your Outlook email normally.
Use the Built-in Media Compression Tool
Outlook has a tool specifically for reducing the size of image and video files you have already attached.
- Attach the media file
Compose a new email and attach your large image or video file using the Attach File button. - Access the File menu
With the email window open, click the File tab in the top-left corner to go to Backstage view. - Compress the media
Select Info from the left menu. Click the down arrow next to “Attachments” and select Compress Media. Choose a size option like HD or Standard.
When the Standard Workarounds Are Not Enough
The Compressed File is Still Too Large
Some files, like high-resolution videos or disk images, do not compress well. In this case, you must use a cloud link. Split the file using a third-party file splitter utility only if the recipient agrees and can reassemble it. For corporate users, ask your IT department about using an FTP server or a dedicated large-file transfer service approved by your company.
Recipients Cannot Access the OneDrive Link
This usually happens because the link permissions are incorrect. When you share, ensure you set the permission to “Anyone with the link” if sending externally, or “People in your organization” for internal emails. If the problem continues, the recipient’s firewall or email security gateway might be blocking access to OneDrive. Ask them to try accessing the link from a different network.
Outlook Says the File is Blocked for Security
Outlook and Exchange Server block certain file types as attachments for security reasons, like .exe or .js files. This is separate from the size limit. You will need to put the file in a ZIP archive or upload it to OneDrive. Renaming the file extension does not bypass this security filter.
Attachment Method Comparison
| Item | Cloud Link (OneDrive/SharePoint) | File Compression (ZIP) | Outlook Media Compression |
|---|---|---|---|
| Best for file types | Any file type, especially very large ones | Documents, presentations, folders | Images and videos only |
| Size limit | Governed by your cloud storage quota | Limited by server attachment policy | Limited by server attachment policy |
| Recipient action needed | Click link to view or download | Download and extract ZIP file | Open email and view attachment |
| File stored on email server | No | Yes | Yes |
You can now send files of any size by using cloud storage links. For future emails, consider setting your OneDrive as the default attachment location in Outlook. A final tip is to use the Outlook on the web interface, which often provides clearer error messages and direct upload prompts when a file exceeds the size limit.