How to quickly unblock unsafe attachment types in Outlook?
If you have received some emails with attachments whose extension is .msi, .exe, etc. in your Outlook, you will get a warning message "Outlook blocked access to the following potentially unsafe attachments" as the following screenshot shown when you open the message. Outlook will consider these types of attachments as unsafe information by default. But, how could you set these attachment types as safe files and easily view or download in Outlook?

Unblock unsafe attachment types in Outlook with modifying the regedit
Unblock unsafe attachment types in Outlook with Kutools for Outlook
Unblock unsafe attachment types in Outlook with modifying the regedit
Normally, you can add the attachment extensions into the "regedit" to allow these specific types of attachments to be safe. Please do as follows:
1. Make sure Outlook is closed.
2. Click the "Start" button of the computer, and in the search box, type "regedit", see screenshot:

3. Press "Enter" key. In the popped-out "User Account Control" dialog, click "Yes" to go to the "Registry Editor" window. In the "Registry Editor" window, locate the following key:
- "Outlook 2010": HKEY_CURRENT_USER\Software\Microsoft\Office\14.0\Outlook\Security
- "Outlook 2013": HKEY_CURRENT_USER\Software\Microsoft\Office\15.0\Outlook\Security
- "Outlook 2016": HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\Security
4. After reaching "Security", click "Edit" > "New" > "String Value", see screenshot:

5. Rename the new item as "Level1Remove", see screenshot:

6. Double-click the created value and enter the extensions including the “dot” that you want to open in Outlook. For example: .exe, see screenshot:

Tips: If you want to enter multiple extensions, separate them by a semicolon, like this: .exe;.bat;.url;.msi.
7. Click "OK" and close the "Registry Editor". Now, launch Outlook. The attachments with these specific extensions won’t be blocked anymore. See screenshot:

Note: If you want to block these extensions again, simply delete the "Level1Remove" value you created in the "Registry Editor".
Unblock unsafe attachment types in Outlook with Kutools for Outlook
If you are confused by the above method, here is an easier way: with Kutools for Outlook's "Safe Attachment" feature, you can quickly set the safe attachment extensions you need.
1. Open Outlook, and click "Kutools" > "Options", see screenshot:

2. In the "Options" dialog box, click the "Others" tab, and then enter the attachment extensions you want to unblock into the "Safe Attachment Extensions" textbox, such as: exe; msi; vbs. See screenshot:

Tips: When typing the extensions, add the dot before each extension, and separate multiple extensions with semicolons.
3. Click "OK". A warning message will pop up, reminding you to restart Outlook for changes to take effect, see screenshot:

4. Click "OK", and restart Outlook to apply the settings.
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