The winmail.dat file contains the Rich Text Format information for the message ... consider what the cartridge maker advises instead. For example, Hewlett-Packard has its own instructions for ...

There are loads of file types swimming around our computers at any given time — most of which exist to supplement the programs we use or play (or allow them to function in the first place).

That winmail.dat file may only be the rich text format (RTF) version of the message you’re already seeing as plain text, in which case all you’re missing is formatting that may not be important.