BoltMail
Signup Confirmation - Double Opt In
Don't get accused of spamming -- always, and I mean always use a double opt-in confirmation process. Double opt-in means that after your visitor initially enters their email address to subscribe to your list, you should then send them a "confirmation" email. This email should contain a special link back to your email marketing program, which will then verify that this visitor did indeed sign up to your mailing list.