To cut a long story short you can trace which email campaign led to which actions by carefully burying address data into email hyperlinks.
This is one I received in my email box
http://www.trailfinders.com/?om_rid=ALdJds&om_mid=_BJw7HjB7gN6rtC&
There are hidden messages in there. An excellent blog article explains Google UTM tags.
Take a look if your interest is EMAIL marketing. Click HERE to go to the BLOG on UTM tags
