How to open a winmail.dat attachment email

‘winmail.dat’ if you get it, is a result of the sender having bad settings on their Windows operating system in their Outlook Express email client. They could fix it and make it go away so you could ask them to do that (and you should) but if you don’t want to waste the time or brain power, there is a nifty online conversion tools:

EDIT AUG 31, 2026 – I found an awesome command line solution to this which I prefer now below, so be sure to read both options and choose best solution for you.

Note: It’s never wise to trust an online conversion tool that could contain confidential information, so consider whether this could negatively affect you or someone else before converting. However, if they are sending you .dat files they are… probably not running a very tight operation anyways…

To convert, go to: this convertor site.

Next, save the winmail.dat file to somewhere you’ll remember on your machine. It would be wise to give it a specific name in case you have other winmail.date files on your machine (ie. you’ve done this before and left the files there…)

Next, browse for that file with the winmail.dat Reader tool with the browse button (above link)

Next press ‘decode’ (green square button)

After it’s done it’s thing you’ll see the body of the email as well as a few links of attachments. There will be, on the right, some green numbers such as 34689 bytes and a little down arrow. That’s what you click to get the attachment. Do that for as many attachments as they are.

Note, it will add a weird random letters and numbers to the front of the file name during conversion but you can adjust the file name later if you want. Save the file wherever you want it and you should be in business.

Option 2 – command line tool (best option)

As mentioned above, it’s not wise to put your confidential communications through someone’s server but I hadn’t discovered the following tool until today, so I want to share this. You have to have some familiarity with linux command lines to do it but it takes all of 2 seconds to convert a winmail.dat file for me now and I can do it on my own local machine so this is now my recommended and preferred way:

1. Download the open source TNEF: sudo apt install tnef
2. Save your winmail.dat file somewhere you won’t forget on your local machine
3. Navigate to it with the cd command in your Terminal / CLI
4. Assuming the name of the file is exactly ‘winmail.dat’ still, run this command in the location where you have it: tnef winmail.dat
   
   If you had renamed to ‘haha.dat’ for example just update accordingly the command to tnef haha.dat
   
   Enjoy!