Change the message text format

[Gautam]

In outlook contacts, I am able to change the text format
to "Plain Text" on individual recipient basis. By doing
this I am able to send attachments through my customized
outlook form.
I tries to change the text format of the outgoing message
Globally, but it didn't worked.
Could anyone please guide me on how I can do this from the
script within the form.
Thank's.
Regards.
Gautam Adlakha