Outlook Not Letting Me Open Attachments? How to Fix It in 2026

When Outlook won’t let you open an attachment, the cause is usually one of four things: the file type is on Outlook’s blocked list, a Windows mouse setting is stopping double-clicks from registering, an add-in or preview problem is getting in the way, or you’ve hit a known bug. Quick test: right-click the attachment and choose Open or Save as. If that works, it’s probably the double-click setting. If Outlook says the file was blocked as unsafe, it’s a blocked file type.

The fixes below are taken from Microsoft’s own support documentation, plus reporting on recent bugs. Menu names and behavior can change, so treat everything here as accurate as of October 2026.

First, figure out which Outlook you’re using

Most fixes depend on which client you have:

• Classic Outlook for Windows is the long-standing desktop app, with a File menu and Options.
• New Outlook for Windows has a simpler interface and no Trust Center. Some classic tools, such as safe mode, don’t apply to it.
• Outlook on the web / Outlook.com runs in your browser.

If you only have trouble in one client, opening the same message in another, for example in Outlook on the web, is often the fastest workaround.

Quick diagnosis table

The attachment is a blocked file type

According to Microsoft’s blocked attachments page, Outlook blocks sending and receiving certain types of files as attachments, such as .exe and some database files, to protect against viruses. The complete list of extensions, including .bat, .cmd and .js, is on Microsoft’s Blocked File Types in Outlook page. Microsoft has expanded the list for Outlook on the web and the new Outlook over the years, so a file that used to come through may now be blocked.

What you can do:

1. Ask the sender to share a link instead. Microsoft’s main recommendation is to upload the file to OneDrive (or a similar service) and send a link.
2. Ask the sender to compress it. Microsoft notes that zipping or renaming the file changes the extension so Outlook won’t block it. You save it, then extract it or restore the original name. Only do this with files you were expecting from someone you trust.
3. On a work account, contact IT. If you use an Exchange account, your administrator controls these security settings and may be able to allow certain types.

Double-clicking does nothing

If right-click > Open works but double-clicking doesn’t, Microsoft Learn puts it down to a Windows mouse double-click speed that’s set too fast. It affects Outlook 2016, 2019 and Outlook for Microsoft 365.

1. Open Control Panel and select Mouse.
2. On the Buttons tab, move the Double-click speed slider one step toward Slow.
3. Select OK and try the attachment again. If it still doesn’t work, move the slider a little further.

This setting applies across Windows, not just Outlook.

New Outlook: double-click opens the desktop app

In the new Outlook for Windows, Microsoft changed double-click behavior in 2024 (Message Center MC844915). Double-clicking now opens the file in your default desktop app, and a single click opens the preview inside Outlook. You may see a confirmation prompt the first time you open each file type. Clear Always ask before opening this type of file if you don’t want to be asked again. If nothing happens, make sure Windows has a default app set for that file type.

Office files stuck in Protected View

Microsoft has documented a known issue where Office attachments in classic Outlook hang at “Opening in Protected View” or show “The file couldn’t open in Protected View.” The cause was traced to certain Intel graphics drivers, and the fix is to update them to version 31.0.101.4887 or later. Microsoft marks the issue as fixed, and the page was last updated in late 2023. Updating your graphics driver through Windows Update or your PC maker’s official site is still worth trying if your symptoms match.

Previews don’t load in the Reading Pane

In classic Outlook, attachment previews are controlled in File > Options > Trust Center > Trust Center Settings > Attachment Handling. Make sure Turn off Attachment Preview is not checked, and that the previewer for your file type is enabled under Attachment and Document Previewers. Microsoft notes that Outlook has no built-in PDF previewer. To preview PDFs you need a PDF app such as Adobe Acrobat Reader installed and set as the default.

Rule out add-ins with safe mode

Safe mode starts classic Outlook with add-ins turned off. Microsoft’s safe mode instructions:

1. Close Outlook.
2. Right-click Start, choose Run, type Outlook.exe /safe and press Enter.
3. Try opening the attachment.

If it works in safe mode, an add-in is the likely cause. Turn add-ins back on one at a time (File > Options > Add-ins) until you find which one breaks it. The new Outlook doesn’t have a safe mode.

Security software can also block attachments it considers suspicious. If your antivirus quarantined the file, check its quarantine or history rather than turning protection off.

“Can’t create file” errors in classic Outlook

Classic Outlook saves a copy of each attachment you open into a hidden temporary folder. Microsoft’s attachment troubleshooting article explains that the folder’s location is stored in the OutlookSecureTempFolder registry value under the Outlook Security key. If that folder fills up with files that have the same name, Outlook can fail to save new copies and you’ll get errors when you open attachments. Clearing out the folder’s contents usually fixes it.

That article was written for older Outlook versions. Before you edit the registry, back it up, and if you’re on a managed work PC, ask IT to do it for you.

Known bugs in the new Outlook

In late 2025, Microsoft confirmed a bug (service alert EX1189359) where some Excel attachments wouldn’t open in the new Outlook when the filename contained non-ASCII characters, such as accented letters or non-Latin scripts. PCWorld reported that a fix was being developed but not yet available to everyone. Microsoft’s suggested workarounds were to:

1. Open the message in Outlook on the web instead, or
2. Save the attachment to your computer and open it from there.

Reports also said classic Outlook wasn’t affected. I couldn’t confirm whether the fix has fully rolled out as of October 2026. If you suddenly can’t open attachments and none of the above fits, check your organization’s Microsoft 365 service health page, or ask your admin about current Outlook incidents.

If nothing works

• Forward the message to yourself and try again. Microsoft has listed this as a workaround for past attachment-blocking issues.
• Save the attachment to your desktop and open it directly from the app it belongs to, such as Word, Excel or a PDF reader.
• Run an Office repair from Windows Settings > Apps (select Microsoft 365/Office, then Modify) to fix damaged program files.
• On a work account, contact your IT team. Many attachment rules are set by administrators and can’t be changed on your PC.