What are .DAT Files?

The .DAT file extension is used for storing data files. Unfortunately, this format is used by hundreds of different programs, all with their own interpretations on how to use place information inside. This means that given two different programs that create .DAT files, you can’t necessarily open the other program’s .DAT file. Rather, you need the program that created the file in question - and it’s not always obvious which program that may be.

For example, I worked for a company that used a point of sale system that generated .DAT files. These files worked fine within the point of sale system but were completely unreadable via other means.

Emailed winmail.DAT Files

Is the file you received named winmail.dat? If so, this .dat file was sent by a user who uses Microsoft Outlook. Outlook uses winmail.dat e-mail files to send the attachment along with the message’s formatting information such as fonts and colors so that the recipient sees the message text as it was intended. However, this only works if the sender and recipient are both Outlook users. The rest of us don’t get an easy-to-open attachment and a message with formatting applied; we get practically unopenable winmail.dat files.

What to Do about Opening the winmail.dat File

You have a couple of options. The first involves asking the sender to resend the message in plain text instead of the default Microsoft Outlook Rich Text Format. The sender should go to Tools> Options and select the Mail Format tab. From there, the sender needs to find the Send this Message Format list and click on Plain Text. In addition, the sender can set up your contact information in his or her Outlook Personal Address book by clicking the entry for your contact information, going to File > Properties, and then clearing the check mark in the box that says, “Always Send to this Recipient in Microsoft Exchange Rich Text Format.”

If you’d rather not send a bunch of instructions to the sender, the other option is to download a winmail.dat decoder. One such decoder is called WMDecode which appears to be free for a limited time or about $10 for non-expiring version. Depending on how often you receive winmail.dat files, you may want to try it out before you buy. Macintosh users can find a similar product called TNEF’s Enough.

If the Attachment is NOT a winmail.dat File

If the attachment is not a winmail.dat file and the sender says that it’s supposed to be a family photo or some other file type, try saving the file to your computer and renaming it, file extension and all. For example, if it’s a photo named familyphoto.dat, try renaming it to familyphoto.jpg. Now try opening it in your favorite image viewing program. If it’s a document file, try renaming it with the .txt format and using Notepad to try to open it. Note, Notepad sometimes successfully opens .dat files, so try it before the change, too. Renaming the .dat file and trying to open it in various programs involves some guesswork and is a bit of a stretch, but it occasionally works so it’s worth trying.

Hopefully, these tips will get that .dat attachment to open for you.

Celeste Stewart | December 5th, 2008
Tags: dat attachment, opening dat files, winmail.dat
Categories: File Extensions

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