download links

Hello: I am trying to do something that seems like it should be very simple but is not turning out to be. I want to be able to put a download link in an email where when person clicks on it (normal click) it opens window to download. Html link wont do it; you have to right click to download on those. I am trying to do this with some nonstandard files like .epub or .mobi

Anyways I am thinking this has to be done in php. It would be great if there was a plugin that could do it. Or some other way; but I am really coming up short. I googled and found some stuff where you put some “header” code on a php but I could not get any of that to work right. can anyone help? thanks, Gerard