Microsoft Outlook Blocks Sending Two More File Types

On Wednesday, October 7, 2026, Microsoft updated its Outlook application to block two more file types from being sent by email. The security update expands existing restrictions on executable attachments, although the exact extensions remain undisclosed until Microsoft confirms them officially.

Why Did Microsoft Outlook Block Two More File Types?

The policy focuses on attachments that can execute code or create security risks when opened. Microsoft hasn’t identified the two newly restricted extensions in the available details, so users can’t yet match the change to specific file names with certainty.

The practical effect is straightforward: users may still compose an email, but Outlook could reject the attachment before sending. The rule applies to the Outlook application, not to every file-sharing service. > An executable attachment can run instructions on a device when opened instead of simply displaying passive content. The number matters because the update adds two file types to an existing restriction list. So what does that mean for everyday email users?

Which Attachments Are Affected by the Outlook Update?

The affected formats fall into the executable or potentially unsafe category, according to Microsoft’s policy description. Since the available announcement doesn’t specify the extensions, users shouldn’t assume that a familiar archive, script, installer, or command file is definitely included.

Businesses may notice the impact first. Developers, IT teams, researchers, and support staff often email tools or diagnostic packages, and a blocked attachment can disrupt work even when the sender is trusted. A safer option is to share the file through an approved cloud-storage link, with access controls and malware scanning enabled. Microsoft’s broader enterprise direction, including Microsoft defines Azure, shows how access governance and security controls increasingly influence everyday software. The next question is whether users can safely work around the restriction. For more detail, see VentureBeat AI.

Can Users Still Send the Blocked File Types?

Users may be able to transfer these files through another approved channel, but changing an extension or hiding a risky file inside an archive isn’t a real security fix. Those tactics can conceal the file’s identity and may lead recipients or security systems to reject it later.

A better process is to upload the file to a managed storage service, scan it, set a limited sharing period, and send a secure link separately. Organisations should also check whether their mail administrator has stricter rules than the standard application policy. This preserves traceability and lowers the chance that an executable reaches an inbox without inspection. The policy’s business impact will depend on how quickly administrators update their sharing procedures.

What Happens Next for Outlook Users?

Microsoft still needs to publish the two file types and explain whether the restriction applies across desktop, web, and mobile versions. Until that information appears, users should view a failed attachment as a policy response rather than proof that the file is damaged.

Administrators should watch Microsoft’s official documentation, review blocked-message alerts, and provide staff with a verified transfer method. Earlier reporting on Microsoft’s AI hardware strategy, including Microsoft NVIDIA’s AI-Centric work, shows how security decisions increasingly accompany broader platform changes. For now, some senders face inconvenience, but Microsoft’s longer-term test will be whether it explains the affected formats clearly enough for businesses to adapt without unsafe workarounds.

The Microsoft Outlook change should make attachment handling safer, as long as Microsoft names the formats and gives administrators clear guidance before users resort to unapproved workarounds.

FAQs

Why did Microsoft block more attachment formats?

Microsoft expanded its restriction policy to target executable or potentially unsafe attachment formats that could expose recipients to security threats.

Were the two blocked file extensions named?

No. The available announcement confirms two additional file types but doesn’t identify their extensions.

What should users do if an attachment is rejected?

Users should use an approved cloud-storage service, scan the file, apply access controls, and send a secure link instead of disguising the attachment.

Does the policy affect every email service?

The announced change concerns the Outlook application. Other email or file-transfer services may follow different rules.