How do I open email attachments in an unknown format on Windows?

Anonymous August 6, 2014
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I receive emails on a Windows PC that I can not open with any of the options on the right-click context menu titled “open with”.

I have recently tried downloading Apache Open Office, but I’m still unable to open certain attachments.

The error message says “unknown format”.

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  1. dragonmouth
    August 6, 2014 at 11:21 pm

    Are the emails from senders you know? Are you expecting these emails? If the answer to both questions is NO, I would treat them as spam and delete them without opening them. In fact, I would set up a filter to delete the emails automatically.

  2. Bruce E
    August 6, 2014 at 9:59 pm

    Relying on the file extension alone to tell you what type of file it is can be risky, especially if you received it from another party. You are better off checking the "magic numbers" in the file header itself to see what it is. You can do this by using the 'file' utility which is part of most *nix distributions and can be obtained for Windows machines through the GnuWin32 pages on SourceForge. It is a command-line tool and you will need to save the attachment somewhere on your hard drive to check it. Once you have 'file' installed on your computer, you will need to make sure that your PATH environment variable contains the path to the 'file' utility (just to make things easier later). Instructions on how to do this are included with the tool. Then open up a command prompt and navigate to where you saved the attachment. Once there, run the command: 'file file_to_check.ext' and it will spit out what type of file it is based on information in the file's header. You can then use this information to determine what program should be used to open it.

  3. Hovsep A
    August 6, 2014 at 7:32 pm

    be sure that the email sender uploaded the file without errors, if error occurred then you will not be able to open the file after downloading to your desktop.

  4. Oron J
    August 6, 2014 at 3:11 pm

    It's really a question of what those files are. If they have file name extensions, then follow Jan's advice.

    If they don't (or you can't see them because they are hidden) then it's best to check with the sender what they are. For example, if you receive a file called "Our holiday" from family friends, you can ask them what type it is and if they say "it's a jpeg" or "it's a pdf" then you can rename the file to "Our holiday.jpg" or "Our holiday.pdf".

    It's difficult to be more specific without knowing what the files actually are, btu this will put you on the right track. Finally, a word of warning. If you receive an attachment (even one which can be opened) from someone you don't know, or without explanation, don't open it until you have verified that it is not malicious. It is trivially easy to create malware and disguise it as an innocent attachment, and this happens a fair bit.

  5. Jan F
    August 6, 2014 at 9:19 am

    Do a right-click Properties on the file. The properties dialog should tell you the file extension ".xyz".
    You can then use an online database like FileExt to lookup the type of file you are dealing with.

    If the file is not too large in size (<5MB or so) you can also open it in notepad.exe as the first few rows of the file often reveal the type or source application.