If recipients of your messages receive an attachment called winmail.dat, you sent messages to them that included Microsoft Exchange Rich Text formatting, such as bold or italic text, but the recipients do not use an e-mail program that can read this format.

To select a message format do the following:

1. On the Tools menu, click Options.
2. On the Mail Format tab, under Message format, in the Compose in this message format list, click HTML or Plain Text.