UTM Tracking

By the use of (Google Analytics) Tracking URL's data streams can be made visible. This way you can see how many website visitors you have acquired through an email newsletter and how many subscribers actually made a purchase.This does require E-commerce and Goals to be set properly in your Google Analytics account however.

You can create your own Tracking URL's here.

After creating a Tracking URL you can reduce the length with tools like bit.ly or tinyurl.com.