A decent portion of the email that I receive is definitely spam, but there are some fringe candidates in my Inbox as well. Often these borderline emails are sent from folks that are legitimately trying to market something to me. As there are email marketing companies out there that are actually concerned about the quantity of spam-flagged emails that are sent from their clients, I always look for an opt-out option before reaching for the spam button.
If I make a web purchase, I sometimes opt-in for future emails. When I receive too much email, I go back and opt-out...easy enough. Occasionally a company decides that I am going to be interested in receiving email from one of their partners and subscribes me to that company's emails. I am not a fan of this, but if there is an opportunity to click an "unsubscribe" link I am not too upset by it.
What I really do not like is when a company shares my email address with a partner that does not give me the option of opting-out. Often they want to force me to create an account on their website so that I can opt-out of receiving future emails. This always leaves me wondering why in the world they would think that I would want create an account when I am already less than please with them for contacting me to begin with?