The use of TNEF is affected by settings in Outlook that are referred to as Rich Text Format (RTF). Outlook can use a special method, technically referred to as Transport Neutral Encapsulation Format (TNEF), to package information for sending messages.
If you aren't expecting an attachment and the file size is too small for an attachment, you don't need to ask for a resend, you are only missing the pretty formatting. This way the sender fixes the problem for future attachments. If there is an attachment in the winmail.dat, asking for a resend is my preference, in most cases. Or ask the Outlook user to resend the file, using plain text format. Don't bother looking in winmail.dat files if you were not expecting an attachment (or if the message size indicates there probably is not an attachment). If you arrived on this page because you received a winmail.dat attachment and don't use Outlook, see the Tools below for utilities you can use to retrieve attachments from the winmail.dat file.
