We have several processes that email logs or other text files to us.
When the extension is .txt, Outlook knows how to show the preview within its main window.
When the extension is .log, Outlook will only offer to open it in an external application, even though we know the file is plain text.
How can I add .log to the list of extensions that Outlook will preview within its main window?
In Windows Explorer right-click any .log file and select "Open With..." -> Choose Default Program. Select Windows Notepad there (not Notepad++) and make sure that you have the "default" check set. Restart Outlook. Not it has to show you .log files.
Update:
If not, check HKEY_CLASSES_ROOT\.log registry key's (Default) value. It has to be "txtfile" (without quotes). The registry change will take effect the next time you log in.
The following should be added in the Registry (it works with Windows 11 and Outlook 2019 as well):
Windows Registry Editor Version 5.00
[HKEY_CLASSES_ROOT\.log]
@="txtfilelegacy"
"Content Type"="text/plain"
"PerceivedType"="text"
