I don't think you can, you can't get information on the mail client of your customer, at my job we code something in php,all we could get is if wether the customer smtp server accepted or not the email we sent him. If the email was accepted, it does'nt always mean it was good since a lot of smtp server are very different, and once the email was delivered to the customer smtp you can't get any other information.
But I have an idea. If your email are in html, you can put a blind link to a server page in it. This page will receive parameter that will be inserted in a table. That way you won't be able to know all who received your email but at least those who opened it.