You go to open a file someone emailed you, and nothing happens. Maybe the attachment shows up as a generic placeholder, maybe double-clicking does nothing, or maybe Outlook flatly tells you it blocked access to a "potentially unsafe" file. Either way, the file is sitting right there in the message and you cannot get to it.
The cause depends on which Outlook you are using (the classic Windows desktop app, the new Outlook for Windows, Outlook on the web, Outlook.com, or the mobile app) and on the file type itself. The good news: most of these are quick, known issues with exact fixes.
Work through the fixes below in order. The first few solve the most common cases in seconds, and the later ones cover the edge cases like blocked file types, full temp folders, and server-side mailbox policies.
Use the Attachment Menu to Download or Save the File
Before assuming anything is broken, try opening the file through its menu rather than relying on the inline preview. Preview and "open the actual file" are two different code paths, so the menu often works when a click does not.
In new Outlook for Windows, attachments sit under the message header in the Reading Pane.
- 1.Select the dropdown arrow next to the attachment.
- 2.Choose Download for a single file, Download all for multiple files, or Save to OneDrive.
- 3.Pick a folder and click Save. You can also drag the attachment straight to your desktop.
In Outlook on the web and Outlook.com, open the message, then select the More actions (three dots) icon next to the attachment and choose Download, Save to OneDrive, or Download all. To edit instead of just open, use the dropdown and pick Edit in Browser or Edit in desktop app.
Right-Click to Open When Double-Click Does Nothing
In classic Outlook for Windows (2016, 2019, and Microsoft 365), double-clicking an attachment sometimes does nothing at all, even though the file is fine. This happens when your mouse double-click speed is set too fast for Outlook to register.
The instant workaround is to right-click the attachment and select Open. To fix it permanently:
- 1.Open Control Panel and select Mouse. If you do not see it, type "mouse" in the search box and select Change mouse settings.
- 2.On the Buttons tab, drag the Double-click speed slider to the left, then select OK.
Moving the slider one step left is usually enough. If double-click still fails, slide it further left and try again.
Route a Blocked File Type Around Outlook
Outlook (both desktop and on the web) blocks roughly 100 file extensions that can carry scripts or code, including .exe, .bat, .cmd, .js, .vbs, .ps1, .msi, .jar, .reg, .scr, .iso, .apk, and .pst. When a file is blocked you cannot open, save, delete, or print it inside Outlook at all; it stays in the email but is completely inaccessible. This same policy applies on the Outlook mobile app for iOS and Android.
The safest fix is to have the sender resend the file in a form Outlook does not block:
- Cloud link (easiest): ask the sender to upload the file to OneDrive or SharePoint and send a sharing link instead of attaching it. In OneDrive they highlight the file and choose Get Link. Have them send the link, not re-attach the file, or it can be blocked again. On mobile, just open the link from the app.
- Zip it: the sender right-clicks the file in Windows and selects Send to compressed (zipped) folder. Outlook does not block .zip.
- Rename it: the sender renames the file to an allowed extension (for example, file.exe to file.docx) and resends. You save it to a local folder, right-click, click Rename, and restore the original extension. Both sender and recipient have to do their half for this to work.
If you are on a Microsoft Exchange Server account, the registry method below will not help you; instead, ask your Exchange administrator to adjust the security settings on your mailbox to accept the blocked attachment type.
Unblock Specific File Types via the Registry
If you are on a non-Exchange account and repeatedly need a blocked type, you can unblock specific extensions in the registry. Back up the registry first, since incorrect edits can cause serious problems.
- 1.Close Outlook, then open Registry Editor (Start > Run > regedit).
- 2.Go to the Security key for your version. Outlook 2016/2019/365 = HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\Security; Outlook 2013 = ...\15.0\...; Outlook 2010 = ...\14.0\...
- 3.Create a new String Value named Level1Remove.
- 4.Set its data to the extensions you want to unblock, separated by semicolons. Current builds use the dotted form (.exe;.com); builds older than 16.0.12923.10000 omit the dot (exe;com).
- 5.Close Registry Editor, restart the computer, then restart Outlook.
Unblock only the file types you absolutely need. A related issue is linked (by-reference) attachments, where Outlook blocks a file stored as a link to a network or local path. For those, create a DWORD value named AllowAttachByRef set to 1 under the same Security key, then restart Outlook. Note this re-enables only ATTACH_BY_REFERENCE and ATTACH_BY_REF_ONLY links; ATTACH_BY_REF_RESOLVE attachments stay blocked.
Clear the Outlook Secure Temporary File Folder
In classic Outlook, opening or saving an attachment can fail with "Cannot create file: <file name>. Right-click the folder...to check your permissions." This means Outlook's secure temp folder is full of files it cannot remove while they are open.
First, make the folder visible. In File Explorer open Folder Options > View tab, select Show hidden files, folders, and drives, and clear Hide protected operating system files (Recommended), then click OK. Both steps are required to see the folder.
- 1.For Outlook 2007/2010, open Run and go to C:\Users\<username>\AppData\Local\Microsoft\Windows\Temporary Internet Files\Content.Outlook
- 2.Open the randomly named subfolder under Content.Outlook (for example, FW0B6RID). There may be more than one such subfolder, so check each.
- 3.Delete the files inside, then reopen the attachment.
The exact folder path is stored in the OutlookSecureTempFolder value under ...Office\<version>\Outlook\Security (version 14.0 for 2010, 12.0 for 2007, 11.0 for 2003). A permanent fix is to install Outlook 2010 Service Pack 1 or the dated Outlook 2007 hotfix.
Switch the Message Format and Check Attachment Preview
If attachments appear jammed inside the message body instead of below the subject line, the message is in Rich Text Format (RTF), which wraps attachments into the body. Preview and the menu actions only work for attachments that sit below the subject line, not for files embedded in the body, so the fix is to change the format.
In classic Outlook, the current format shows in the title bar; switch the message to HTML or Plain Text. In new Outlook, use Options > Format on the ribbon, which toggles between Switch to plain text and Switch to HTML. Use HTML so shared links stay clickable rather than showing as non-clickable copies.
If a specific preview is failing, you can disable previewers. Go to File > Options > Trust Center > Trust Center Settings > Attachment Handling. Select Turn off Attachment Preview to disable all preview, or click Attachment and Document Previewers, clear the checkbox for the problem previewer, and click OK. You can then still open the file via the menu.
Send Oversized Files as a OneDrive Link
On Outlook.com, the maximum total email size is 25 MB, counting text, inserted files, and attachments together. Resizing an image does not reduce its file size, so a large file simply will not attach. The fix is to send it as a OneDrive link.
- 1.In a new message select Attach, then choose the file from OneDrive, or choose Upload and Share.
- 2.Select Share link. The linked file can be up to 2 GB and does not count toward the 25 MB email size limit.
You can also use Copy link on a OneDrive or Office file and paste it into the email. Two things to keep in mind: replying to a message does not carry over its original attachment, and you can only attach files to calendar events you or a delegate created.
Fix Server-Side Blocks on Web and Shared Mailboxes
On Outlook on the web for Microsoft 365 or Exchange, an attachment may show as a generic "1 Attachment" placeholder or error with "Access to attachments has been blocked. Blocked attachments: <FileName>." The file's extension is on the mailbox policy's blocked list. An administrator can remove the extension from the blocked lists and add it to the allowed lists in Exchange Online PowerShell (for example, Set-OwaMailboxPolicy -BlockedFileTypes @{Remove='.xml'} followed by -AllowedFileTypes @{Add='.xml'}). The change can take several minutes and increases security risk; if it cannot be changed, have the sender send the file as a .zip.
A separate bug hits shared or additional mailboxes on on-premises Exchange Server, producing "Something went wrong while the document preview was being created. Please try again later." This affected Exchange 2019 CU7 and Exchange 2016 CU18. The permanent fix is installing Exchange Server 2019 CU8 or later, or 2016 CU19 or later. As a workaround, open the attachment from the additional mailbox using the Outlook desktop client, or use the OWA light version by appending ?layout=light to the mailbox URL.
Frequently Asked Questions
Why can I see the attachment but not open, save, or delete it?
The file type is on Outlook's blocked list of unsafe extensions. When a file is blocked, every action inside Outlook (open, save, delete, print) is disabled. The file remains in the email but cannot be touched; you have to get a safe copy via a OneDrive link, a zip, or a renamed file.
Double-clicking my attachment does nothing. Is Outlook broken?
No. In classic Outlook for Windows this is almost always the mouse double-click speed being set too fast. Right-click the attachment and choose Open for now, then slow the Double-click speed slider in Control Panel > Mouse to fix it for good.
I tried the Level1Remove registry edit but my attachments are still blocked.
The registry unblock method only works for accounts that are not on Microsoft Exchange. If you are on an Exchange account, your administrator has to adjust the mailbox security settings instead. Also confirm you used the right extension format: builds older than 16.0.12923.10000 need the extension without the leading dot.
Where does Outlook save my attachments, and why are there duplicates?
The default save location is the Documents folder, and it cannot be changed system-wide. When you save a file with a name that already exists, Outlook appends a number rather than prompting to overwrite, by design, so copies can pile up.
My edits to an attachment keep disappearing. How do I keep them?
Edits are only preserved if the file lives in cloud storage. If the sender did not use OneDrive, use the attachment dropdown and choose Save to OneDrive before you edit, so changes save automatically.
Does the same blocking apply on the Outlook mobile app?
Yes. Outlook for iOS and Android applies the same attachment-blocking policy as the desktop and web versions. The workaround is the same too: have the sender upload the file to OneDrive or SharePoint and send a link, then open that link from the app.
