It is easy. You might have a problem here however with people using the server then to spam.
you would need a speedlimit or a submission feature.
But anyhow, there is the feature to send a story to someone already. it also includes all the speedlimit. I guess the internam mail function COM_mail does the limit automatically?
I have written some static page forms that send emails, such as a reservation form for a restaurant. basically it revolves around using
Text Formatted Code
$result=COM_mail ($receiver-email, $title, $message,'', false, 0);
It is quite easy to make a function and include it into lib_custom.
If you have big trouble writing that yourself tell me.