What is an .unknown extension file type, you ask? Well, chances are you never even heard of this file format but that doesn’t mean it doesn’t exist! The files with the file extension of .unknown are basically not associated any particular type of file, folder, program or software and hence the name ‘unknown’ . These are the unknown Windows files which do not consist of a file association. However, these are very rare files and are not witnessed every day. They are generally created by the Microsoft Mail Program. This program is launched as the successor to the Microsoft Outlook program. When the Microsoft Mail receives a file which it is not able to identify, then by default, the extensio n of the file becomes .unknown.

So, why is a file name as .unknown?

The reasons why a file may have the UNKNOWN may be because the file was not properly transferred on the web because it was corrupt. Another reason might be that the file was not uploaded completely and with proper mechanism on the mail. These factors make it difficult for the programs to identify such files. It might be that the file has not passed through the gateway properly. There might be security reasons behind it or even the policies of some companies or associations which purposely block some types of files.

Things to know

If a file gets converted to the UNKNOWN, then it cannot be recovered or viewing the contents of the original parent file won’t be possible by any means. An unknown file is of no help as the user cannot retrieve the data lost through it. However, some of these files may open with some of the text editor programs. If this is the case, then the contents of the file can be viewed and edited using a text editor. However, if the files are in the binary format, then opening them with the text editor also will not help.

There is one way of knowing the actual file extension of an .unknown file. It can be done by identifying the unique signature of the file which is included in the file itself. Then, these signatures can be determined through different software online which can tell the exact file extension – even if the file extension is actually missing. Although the files with the .unknown extension cannot be recovered fully; their suitable extensions can be known so that they can be opened with a suitable program later.

Open UNKNOWN File on Windows OS

  • Look for an UNKNOWN file you need to open in Windows Explorer and double-click on it
  • If the file doesn’t open automatically and you see a “Windows can’t open a file” message then you should search for a program which can open UNKNOWN file
  • If you have a program which can open UNKNOWN file installed on your computer then launch that program and select “File” and then “Open” or similar options from its menu to open the UNKNOWN file
  • If you don’t have the program installed then you need to try searching for “UNKNOWN wiki”, “how to open UNKNOWN file” in the search engine.
  • Once you find the application, install it on your computer
  • After the program is installed double-click on the UNKNOWN file to open it

File extensions are used by Windows operating system to specify what kind of information is stored in the file. Every file in Windows OS needs to have file extension and file extensions are used by Windows to determine which application it should use to open the file. Every application installed on Windows OS places information about which extensions it could open into the Windows registry and Windows uses this information to determine which application it should launch when user double-clicks on the file. If application which can open UNKNOWN file is not installed, then Windows will show ‘Windows can’t open UNKNOWN file’ message and buttons to either select an application on the computer which can open the file or to search the web for the application which can open UNKNOWN file.