If Outlook blocks a file, the recommended option is to upload it to OneDrive or a secure SharePoint location and email a sharing link. Make sure the recipient has permission to open the file. You can also try sending a ZIP archive; renaming the file extension is another documented workaround, but neither method makes a file safe.
Why Outlook blocks some attachments
Outlook blocks certain file types to help protect senders and recipients from computer viruses. The exact controls can differ between New Outlook, classic Outlook for Windows, Outlook on the web, Outlook.com, and mobile versions, so use guidance for your specific client. See Microsoft’s Blocked attachments in Outlook and Windows attachment troubleshooting.
Best option: share the file from OneDrive or SharePoint
Microsoft describes a OneDrive or secure SharePoint link as the simplest way to send a blocked file. It avoids attaching the blocked file itself and lets you manage who can access it.
- Upload the file to OneDrive or an appropriately secured SharePoint location.
- Create a sharing link and set permissions so the intended recipient can access the file, granting only the access needed.
- Email the link to the recipient. Where practical, confirm they can open it.
- If they cannot open it, review the link’s permissions and access settings. A link to a location only you can access will not work for them.
Microsoft’s guidance on adding files to Outlook email notes that recipients may not be able to view a link to a location available only to the sender.
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Alternative: attach a ZIP archive
Compression changes how a file is packaged; it does not remove malware or prove that the contents are trustworthy. Microsoft documents using a compression utility, such as WinZip, to create an archive with a different extension. On Windows, its troubleshooting guidance also gives a built-in option:
- In File Explorer, right-click the file.
- Select Send to > Compressed (zipped) folder.
- Attach the resulting ZIP file to your Outlook message if Outlook accepts it.
Microsoft covers this approach in its guidance on blocked file types and troubleshooting Outlook attachments for Windows. Do not assume a ZIP will get through: organization rules or Outlook controls may still block it.
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Alternative: rename the file extension—with caution
Microsoft also documents changing a blocked file’s visible extension to one Outlook does not block, sending it, and asking the recipient to save the attachment and restore the original extension. This changes the filename, not the file’s underlying contents, and it is less transparent than sharing a link.
- Use this only for a file the recipient is expecting and trusts.
- Rename the file with an extension Outlook accepts and send it.
- Tell the recipient what the original extension was and to save the file before restoring that extension.
- Ask the recipient to verify an unexpected file with you before opening it.
Changing an extension is not a security fix. Microsoft advises caution with attachments, particularly those from unknown or untrusted senders; see its attachment safety guidance and blocked-attachment guidance.
Which option should you use?
| Option | Security and transparency | Recipient access | When it fits |
|---|---|---|---|
| OneDrive or SharePoint link | Preferred approach; use a trusted location and appropriate permissions. | The recipient must be granted access to the linked file. | Best default for sending a blocked file. |
| ZIP archive | Changes packaging only; does not establish that the contents are safe. | The archive must be accepted by Outlook and the recipient must be able to open ZIP files. | A convenient alternative when permitted. |
| Renamed extension | Less transparent; the file contents are unchanged, so use only for an expected, trusted file. | The recipient must know the original extension and restore it after saving. | A limited workaround when other options are unavailable and policy permits it. |
| Ask an Exchange administrator | Depends on the organization’s configuration and policy. | The administrator may be able to adjust handling for certain file types or mailbox attachment settings. | Use when other methods are unavailable or blocked on an Exchange account. |
When to contact your administrator
If you use an Exchange account and Outlook still blocks the file, ask your organization’s administrator whether its attachment settings or policy allow another route. Microsoft says an Exchange administrator may be able to unblock certain file types or adjust mailbox attachment settings. Do not treat registry changes as a routine end-user fix; organizational policy may also restrict cloud links and ZIP archives. See Microsoft’s Exchange attachment guidance.
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