mail function headers

[mouli]

Hi
I have a small script that sends email from a form using the mail function.
The recipient is using Outlook.
If I set the content-type header to:

text/plain; charset=us-ascii

the email gets through but obviously as plain unformatted text.

However if I set the content-type header to

text/html; charset= iso-8859-1

they receive a blank email with the original content attached as a .dat file

Any ideas would be much appreciated as they'd like the emails received with active links etc.

Many thanks

mouli