MS Outlook will sometimes send attachments wrapped up in winmail.dat files. This is not a common format, and other users may not be able to open these files.

If you are using Outlook - avoid sending emails in the RTF (or Rich Text) format. Instead use the universal standards of HTML.

To change this setting, in Outlook 2003...

Step 1: Under Tools/Options...


Step 3: Mail Format Tab, Select HTML


Step 3: Click the "Internet Format..." button and select "Convert to HTML format"