If I understand correctly you want to count which emails are read. If they are HTML emails, this is fairly easy to do. The general technique is the same as counting any HTML page.
The easist way is to include a transparent 1x1 pixel image and write a script to process the request:
img src="ht**://www.somesite.com/countme.asp?parm=xxx"
** is tp and the brackets are missing. mycount.asp is a script that will do the counting and return the image. The parm may be something like emai1234.
Javascript can be added to the HTML to do the same thing. Here you make what looks like a remote Javascript load and it is really just another way to call mycount.asp.
With a little work you may load a fake CSS script in place of the one-pixel image. If you call your logo or a banner by going to a script rather than a page, the need for a one-pixel image also can be avoided.
Anyway you can call your server during page load time works.
There are commercial packages that can do this, but if all you want is a count it is easy in ASP. When you want to tie together the read, a resulting click-thru and a sale or registration things get more complicated and the package solution is probably better.
With email being filtered with spam filters, I feel every newsletter should be tracking their opens. A 40% open rate is considered golden and few newsletters are getting even getting that.