If I haven't done business with you before and recieve email from you it won't matter who's service you are using. You'll never get an email inside my network again. That is the scenario you face.
people sign up. I'm given the list (part of my paid advertising with the show), so it isn't completely random.
Constant Contact works well. Have used it for the last three + years. The list is 6 digits large now, started much smaller. Their service has worked well each step along the way.
Not sure of their costs for smaller lists, but SilverPop is a good company and can help you expand past email. www.silverpop.com