To ensure your emails get delivered, always use doube opt-in

Double Opt in is a process whereby once the subscriber submits their name and email, a follow up email is sent to the subscriber requiring a confirmation of their subscription to your email program.  This is usually in the form of a click on link.  Although double opt in processes reduce the size of your email list, they ensure the quality of the list.  A quality list is your best resource for email marketing purposes