Off topic rant, but in my personal experience brands destroy more value/goodwill on their email marketing campaigns than any incremental sales they generate. Why even give me the option to not sign up for your email marketing list when I check out if you’re going to spam me anyway?
The point is to drive business to the company and that is what should be measured. If people click on your email but don't do any purchase they were already about to make, they are useless. If your spam also alienate your customers, stop what you're doing, no matter your open rate!
I don't understand how so many companies let their marketing department get away with this.