I friend of mine recently ran into a problem, where she had received an email-message with just one file, named winmail.dat, as attachment. Basically, she expected to be able to view a message with an attached file (an Illustrator-file). But all she got was this winmail.dat.
After some investigation, I found out that this has to do with the combination of Outlook (on the sender side) and Microsoft Exchange on the server side of the sender of the email message. According to what I found out, the following happens:
If you have stated in your Personal Address Book (or in the message settings directly), that the recipient of your message can handle messages in Richt Text Format (RTF), then Exchange wraps this message in the above mentioned winmail.dat file for the mail client of the recipient to decode. Unfortunately, if, for some reason, the recipient cannot handle RTF-files (or is just not capable of handling winmail.dat files), the message becomes useless to the recipient. Microsoft has published an article in its support knowledge base, discribing several methods to solve this problem.
There are also some tools available for free, which are able to open a winmail.dat-file, display the message and even let you save any attachments that were part of the original message. I tried WMViewer and Winmail Opener. From my experience, I’d say that Winmail Opener is the tool to go, as only this one was able to also display the attached file.
Akeesoft provides some nice Q&A on their site about this topic:
Hi
Another way to open those attachments is to use an online converter like http://www.winmaildat.com . But for attachments with sensitive data that might not be a good idea.
Cheers