Ever received a mostly-blank email that contained an attachment called "winmail.dat"? Or maybe you sent one and cursed the foolish recipient for gibbering on about some winmail.dat file when you know you didn't attach such a thing.

If so, no hallucinations necessarily took part in that experience. It's another treat from the Microsoft guys. On occasions Microsoft Outlook will try and send the message all nice and pretty in some weird-ass Microsoft Transport Neutral Encapsulation Format (MS-TNEF) that not much else understands. This is an attempt to convey formatting information such as fonts, colours and all the rest of the modern jiggery-pokery that largely is a distraction from the actual content of the email. If the recipient's program doesn't understand what MS-TNEF is (i.e. it isn't Outlook) that the formatted version comes as an attachment called winmail.dat. No big deal - except that if you have deliberately attached a file to the email (e.g. a PDF file, a Word file and so on) then that is also hidden inside the MS-TNEF winmail.dat file and as such any programs that don't do the MS-TNEF malarkey can't even see the attached file, let alone open it.

The solution? Arguably the best thing to do is call up the sender and tell them you only want to receive plain-text formatted emails. There are easy (but not the default) options in Outlook to do this on a per message, per recipient or a more universal basis. A quick way that fixes it for everyone you intend to email is to go to the Tools menu, pick Options then Mail format and in the resulting window select to send plain text only. From now on no-one the sender emails should ever get a winmail.dat.

However if the sender is reticent - or too stupid - to do this in case they sacrifice the ability to write vomit-inducing coloured flashy emails to their friends who have bought into the Microsoft way, then all is not lost. You, as the receiver, can decode the winmail.dat file and get the attachments out. You just need help from other software.

Probably the simplest thing to do if your file isn't too large (less than 4MB) is go to the MS-TNEF Degenerator website. This handy website allows you to upload the winmail.dat attachment and will extract and return you the files contained within it. It is powered by the opensource project TNEF which you can download onto your own computer if you are OK with dealing with source code and want more flexibility or privacy than the Degenerator site provides. If none of that's good for you there is the odd Windows or Mac program out there that does the same job; including WMDecode and TNEF Enough.