While opening an attachment in the Outlook desktop app if you see the You should only open attachments from a trustworthy source warning message, the solutions provided in this article will help you. This is not an error message. It is a warning message that alerts users while opening an attachment in Outlook.
You should only open attachments from a trustworthy source message in Outlook
When the You should only open attachments from a trustworthy source message appears in Outlook, you will see the following three options:
- Open
- Save
- Cancel
You can select any of the above options. If you want to open the file, click Open. As explained above, this is not an error message. It is a warning message which can appear while opening any attachment, like an Excel file, a Word file, a PDF file, a compressed folder, etc. Hence, it may irritate you because it appears whenever you open an Outlook attachment. Many users found this message frustrating and want to disable it. Here, we will show you some fixes that will help you disable this warning message in Outlook.
- Disable the “Always ask…” checkbox
- Change the Trust Center settings
- Uninstall and reinstall the required program
- Modify Windows Registry
Let’s see all these fixes in detail.
1] Disable the “Always ask…” checkbox
I also experienced this issue on my Outlook desktop app. When I tried to open the PDF files, it displayed me the “You should only open attachments from a trustworthy source” warning message. I was able to disable this message by unchecking the “Always ask…” checkbox.
When you open an attachment in Outlook, it displays the warning message in question. This warning message also has an “Always ask before opening this type of file” checkbox. This checkbox is enabled by default. You have to deselect this checkbox and click Open. After that Outlook will not show you this warning message when you open that particular file type.
If the checkbox is greyed out, open Outlook as an administrator and then uncheck the checkbox. After that, open the file. To open Outlook as an administrator, right-click on it and select Run as administrator. Many users also confirmed that this simple fix has resolved the issue for them.
2] Change the Trust Center settings
This solution is for Microsoft Word, Excel, and PowerPoint files. If Outlook shows you the warning message while opening Word, Excel. or PowerPoint files, changing the Trust Center settings can help. Enable the Protected View for Outlook attachments in Trust Center settings for Word, Excel, and PowerPoint. The following steps will help you with that:
- Open Microsoft Word.
- Go to File > Options > Trust Center.
- Click Trust Center Settings.
- Select Protected View from the left side.
- Select the “Enable Protected View for Outlook attachments” checkbox.
- Click OK to save the changes. Click OK again to close the Outlook Options window.
You have to enable this option for Word, Excel, and PowerPoint separately by opening each of these applications. When you are done, restart Outlook (if it is already opened).
3] Uninstall and reinstall the required program
For some users, uninstalling and reinstalling the affected application fixed the problem. For example, if you see a warning message while opening the PDF file in Outlook, uninstalling and reinstalling the PDF Viewer software can help.
4] Modify Windows Registry
If none of the above solutions fixed the issue, the last option is to modify Windows Registry. This fix requires Registry modification. Hence, proceed carefully and modify only the correct values or keys. Any mistake while modifying in Windows Registry can make your system unstable.
Before you proceed, we recommend you backup the entire Registry and create a System Restore Point.
You have to modify the values of keys related to different software or applications under the Office key in the HKEY_LOCAL_MACHINE Registry Hive. But before this, you can try modifying the value of Outlook.File.oft.15 key, as it worked for some users. If this fix works, you need not modify different keys for different software or applications in Registry.
The following steps will show you how to open the Registry Editor.
- Open the Run command box (Win + R).
- Type regedit and click OK.
- Click Yes in the UAC prompt.
When the Registry Editor opens up, Copy the following path and paste it into the address bar of the Registry Editor. After that, hit Enter.
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Office\ClickToRun\REGISTRY\MACHINE\Software\Classes\Outlook.File.oft.15
Make sure that Outlook.File.oft.15 key is selected on the left side. Now, double-click on the EditFlags Binary Value on the right side and then change the third digit to 01. This will disable the message warning message in Outlook for attachments. Click OK to save changes. Close the Registry Editor and restart your computer.
If this does not work, revert the changes you have made above and edit the flags for different software and applications under the Office key. You have to change the EditFlags Binary Value to 00 00 01 00. This should disable the warning message for that application.
Open the Registry Editor and go to the following path:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Office\ClickToRun\REGISTRY\MACHINE\Software\Classes
Now, here you have to apply the Hit and Trial method. So, change only one key at a time and then see if the problem disappears. If not, revert the changes and then modify another key. This will take time but works.
Let’s assume that Outlook is showing the warning message for Microsoft Word documents. Now, in this case, you have to modify the EditFlags Binary Value for the following keys under the above-mentioned path.
- .doc\Word.Document.8
- .docx\Word.Document.12
- Word.Document.8
- Word.Document.12
For the above-mentioned keys, there should be the EditFlags Binary Value on the right side. If the value is not there, right-click in the empty space on the right side and select New > Binary Value. Name this newly created value as EditFlags. Now, double-click on the EditFlags value and change its value to 00 00 01 00. Click OK to save the changes. restart your computer and see if the problem persists. If this does not work, revert the changes and change the EditFlags Binary Value for another key.
Read: Drafts not saving in Outlook; Recover Draft Emails in Outlook.
How do I turn off the attachment security warning in Outlook?
You can turn off the attachment security warning in Outlook by disabling the “Always ask before opening this type of file” checkbox. For Microsoft Word, Excel, and PowerPoint files, you can do the same by changing the Trust Center settings.
Why are PDF files not opening in Outlook?
It is possible that you have not installed any PDF viewer software or you have not selected PDF viewer software as a default software to open the PDF files.
Read next: Polls not working in Outlook.
