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The safest general option is to upload the file to OneDrive or an organization-approved SharePoint location, then send a sharing link. Set the link for the intended recipients, review whether they can edit or download the file, and remove access when they no longer need it. Microsoft recommends this approach for file types Outlook blocks.
Why Outlook blocks some attachments
Outlook blocks certain file types as a security measure because attachments can carry computer viruses. Microsoft lists examples such as .bat, .exe, .vbs, and .js; these are examples, not a complete list. See Microsoft’s blocked file types in Outlook guidance.
The exact restrictions can depend on the Outlook product and your organization’s settings. Work or school accounts may also have SharePoint file restrictions or rules against external sharing. Microsoft describes some of these limits in its OneDrive and SharePoint restrictions and limitations.
Best option: share a OneDrive or SharePoint link
Microsoft’s Blocked attachments in Outlook guidance says: “If you need to send one of these file types to an email recipient, we recommend using OneDrive and sending the recipient a link to the file instead.” For work or school files, use the storage location approved by your organization.
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- Upload the file. Put it in OneDrive or the appropriate SharePoint location, subject to your organization’s rules.
- Create a sharing link. Choose the narrowest access option that suits the recipients. If available, select “Specific people” and invite the intended recipients.
- Review permissions. Remove editing access if recipients only need to view the file. For supported view-only links in OneDrive for work or school, “Block download” may be available; the option can be disabled or unavailable for some accounts.
- Send the link and verify access. Check that the link settings match your intent and, for sensitive files, confirm that recipients can open it from their account context.
- Remove access when it is no longer needed. Use Manage access to remove people or stop sharing.
Microsoft explains link types and permission management in its guidance on external or guest sharing in OneDrive, SharePoint, and Lists and blocking downloads for view-only files.
Choose a link that fits the file
- Specific people: Limits access to the people invited, when the option is available and permitted by the organization.
- Anyone: Can be forwarded; anyone who gets the link may be able to access the content. Avoid it for sensitive files.
- View or edit: Sharing links may allow editing. Give edit access only when recipients need it.
- Block download: Consider this for supported view-only OneDrive for work or school links if the setting is available and suitable. It is not available for every account or link.
How the alternatives compare
| Method | Access control | Recipient experience | When it makes sense |
|---|---|---|---|
| OneDrive or SharePoint link | Permissions can be managed; available controls depend on the account and organization policy. | Recipients open the link and may need to sign in or have access granted. | Recommended default, especially for work or school files. Confirm the intended recipients can access it. |
| ZIP or other compression | Does not make the enclosed file safer; it only changes how the file is packaged. | Recipients must extract the archive and handle the original file. | Microsoft documents it as a workaround, but it is not a security protection. |
| Rename the file extension | Does not change what the file does and may bypass an extension-based block. | Recipients must know the original file type and restore or interpret the extension correctly. | Microsoft documents this workaround, but a controlled sharing link is the better default. |
| Ask an administrator about an exception | Any change is governed by organizational policy. | May allow an approved file type, but is not an end-user setting. | Use when a legitimate business need is blocked and the organization’s administrator can assess it. |
Why zipping or renaming is not a security fix
Microsoft documents compression and extension-renaming workarounds in its blocked attachments guidance. Neither method changes the underlying file into a safe one. A ZIP archive still contains the original file, and a renamed file can still behave according to its actual format. Use these methods only when the recipient is trusted and understands what the file is; do not treat them as protection against malware.
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Microsoft’s older guidance on potentially unsafe Outlook attachments discusses security settings, but changing registry or security settings is not a routine workaround for ordinary users. If an attachment has a legitimate business purpose, ask the administrator to review the policy instead.
What to do if the link or upload is blocked
- Check whether the file type is restricted in the organization’s OneDrive or SharePoint environment.
- Check whether external sharing is allowed and whether the recipients have been granted access.
- Ask the sender or the organization’s administrator for an approved transfer method or policy exception.
An administrator may be able to allow selected attachment types in Exchange, but that is an organizational security decision, not a personal Outlook fix. Microsoft’s blocked attachments guidance describes this possibility.
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Check the file before opening it
A link, ZIP archive, or renamed filename does not prove that a file is safe. Before opening a blocked file, verify that it came from the expected sender and that you were expecting it. If you are unsure, confirm with the sender through a separate trusted channel or ask your organization’s IT administrator. Microsoft’s general guidance on opening, saving, and editing Outlook attachments also explains attachment handling.
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