Error viewing .msg (Outlook) files (Opus and Explorer)

I save my important Outlook e-mail as .msg files. Every time I double-click on a saved Outlook e-mail, this error message pops up: "Either there is no default mail client or the current mail client cannot fulfill the messaging request. Please run Microsoft Outlook and set it as the default mail client." Of course, I have set Outlook at the default mail client everywhere possible, and I set .msg files to be openable by Outlook. These error messages do not occur when I double-click on .msg files in Windows Explorer. They do not occur in Opus when I right-click on a ,msg file and click on Open with Outlook 2016. To get rid of the error messages, I must delete them twice. I click on OK and then another one pops up.
If I double-click on a second message file, 4 error messages appear and Opus stops working. All other files associations work fine with Opus. HELP!

Please do the following to generate a dump of the relevant file type detials:

  • Go to Settings > File Types.
  • Select File > Diagnostic from the menus in the File Types dialog.
  • Enter msg as the extension and click OK.

It should create a zip file on your desktop which you can attach here or via a private message. (It usually won't contain anything private, but it's always possible, so you might prefer using a private message.)

After doing that for us to look at, you may find that this functions as a workaround:

  • Go to Settings > File Types again.
  • Expand the System File Types section, and find the MSG file type in the list.
  • Double-click the MSG type to edit it.
  • Select the Events tab and double-click the Left double-click event.
  • Paste this command into the big box:
    FileType ACTION=open
  • Click OK in each of the dialogs.

That should make double-clicks work for now, if right-click > open was working before. (35.4 KB)


I followed these orders for the workaround:

Go to Settings > File Types again.
Expand the System File Types section, and find the MSG file type in the list.
Double-click the MSG type to edit it.
Select the Events tab and double-click the Left double-click event.
Paste this command into the big box:
FileType ACTION=open

Unfortunately, nothing has changed. Every time I double-click a file with the .msg suffix, this error message pops up. I click OK and it pops up again. I click OK again and it goes away. If I right-click the same .msg file and then click on Open With Outlook, it opens without the error message. If I double left-click on that same file using Windows Explorer, it opens without the error message. But I use D.O. for all my work, and I want to fix this. Incidentally, I still have D.O. on my former computer. This problem does not exist there. The only difference that I can see that the old computer has the 32-bit version of Outlook and the new computer has the 64-bit version.

In your e-mail to me, you told me to create and send you a .zip file. I did that yesterday. But now I notice that I replied to your e-mail and attached the .zip file. Your e-mail address was So I am guessing that you did not receive the e-mail with the .zip file attached.

I see a button at the top of this screen called Upload. I will see if that will allow me to send you the .zip file. Please let me know.

Thank you,


Many thanks for the diagnostic file.

The error you are seeing, does it only happen if the viewer pane is open?

Leo, you're a genius! I use that viewer pane constantly, and it did not occur to me to turn it off. When I turned it off a moment ago and then double-clicked on .msg files, the error messages DID NOT appear. Is there a way that I can turn the viewer pane back on but avoid those annoying messages?

You should be able to work out which viewer is causing the messages and repair or disable it.

First thing: Does the same happen with the viewer in File Explorer?

Hello again.
I opened File Explorer and found the button that turns on the “Preview Pane.” When I turned on Preview Pane and then clicked on a .msg file (just single clicked), the error message appeared.
So why does this NOT happen on my old (only 1 year old) Microsoft Surface computer?
Does some setting need to be adjusted on my computer? Or is there some way that I can tweak the viewer on DO to stop this annoying problem?



I just noticed that I don't need to double-click on a .msg file to generate the error message. When the viewer is on, I need only single-click on a .msg file, and the error message appears twice. Same happens in File Explorer.

Unless you've got a solution, I suppose that the answer is that I must turn off the viewer before clicking on .msg files. I wonder why this does not happen on my Microsoft Surface computer.


Yes, the error is coming from Microsoft's .MSG viewer which is part of Windows, but also talks to Microsoft Outlook if it is installed. It'll happen on selection when the file is loaded into the viewer, and double-click won't be involved.

I've updated the thread title accordingly.

You would have to ask the Microsoft that, since it is their viewer. :slight_smile: Something else that deals with .MSG files has probably messed up some registry settings.

According to this, a full uninstall and reinstall of Office has fixed the same viewer issue on several people's PCs.

If you don't care about viewing .MSG files in the viewer, and don't care about Explorer, and just want to disable the broken .MSG viewer within Opus, you can do that as follows:

  • Go to Settings > Preferences / Viewer / Plugins
  • Select the ActiveX + Preview + Office + Web plugin and click Configure
  • In the Preview Handlers section of the list, find the one that .msg is assigned to. It's usually Microsoft MAPI (32-bit).
  • Turn off that viewer by clearing the checkbox next to it, then click OK.

But if you want the viewer to work for .MSG files, repairing or reinstalling Outlook sounds like the way to go.

Leo, I owe you dinner in San Francisco! You just solved my problem. I don't need to see the .msg files in my viewer. I followed your instructions. The .msg file no longer appears in the viewer, but that's fine. It's too small to read there anyway. The error messages are gone.

You are a star! Many thanks.


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