A: 

We had a similar problem. Couldn't figure out who's stripping the html and why, but we discovered that adding a <font> tag (yes, the ancient deprecated one) leaves the content type as text/html and includes the full formatting.

Can anyone shed more light one this?

Doron
A: 

Including the <STYLE/> in the <BODY/> of your HTML should do the trick.

mwiessenberg
A: 

I confirm that including the STYLE block inside the BODY block seems to work.

Nicolas Buquet