I’ve seen several questions recently about winmail.dat attachment files that come with some emails.
If you use an email program that stores attachments in a different folder than it stores the actual emails (Eudora, which I use, is one), you can find that you collect a lot of Windmail.dat attachments.
When we try to open them, they seem filled with gibberish.
But, what are they?
A winmail.dat file is attached to an email sent from Microsoft Outlook, if the Outlook user has formatted the email using Rich Text Format. The winmail.dat file contains all the formatting details like font size, which font, bold or not, details on the "Stationery" and more.
Unfortunately, Outlook’s default format for Internet email is to format using Rich Text Format! Since the only people who can actually use a winmail.dat file are those who are using Outlook, it just shows up as another attachment for everyone else.
Fortunately, you can change the default email format in Outlook — you can choose RTF, HTML or plain text. Most people prefer to receive plain text. You can also change each individual message to send in RTF, HTML or plain text.
If you’re using Outlook and don’t know how to change the default setting for the formatting, read my article Choosing to Send Plain Text or HTML in Outlook Emails.