Mail Formatting lost when sending from Panther "mail" app.

Powerbook G3 (firewire version)
OSX Panther 10.3.5

When I compose mail with formatting, such as color text, center text alignment, url links, inline pics, etc., some people, but not all, that I send mail to respond saying all formating was lost (receiving plain text only).

Also, when composing mail I can not set a background color - that function simply does not work. I can set font color however.

I can use Explorer of Netscape with no such problems.

Any thoughts appreciated, Nick