[plt-scheme] plt web server serving .eml files as text/html

Hi,

I'm using the plt web server, and I have some static files (email
messages in .eml ) that I want the browser to pass on to thunderbird
mail client;

When I put them behind the plt webserver they get shown by the browser
(as text/html), but under apache, or even as a local file in the
browser they get passed to thunderbird.

Is there any way to convince the plt-web server let firefox know they
should go to thunderbird? (I'm pretty sure  text/html Content-Type is
the problem)

Thanks,

Stephen