1) Send a follow-up email thanking new registrants or subscribers for signing up.
2) Require a double opt-in. This means both asking for the initial email address (and whatever additional information you need), and then sending an email to that address requiring that the person confirm their subscription. This can be done automatically.
3) Send an email within thirty days of the initial signup, with the first installment, issue, etc. If you wait longer, people will forget they signed up.
4) Include an unsubscribe link at the bottom of every email, as well as your physical address (this can be a P.O. box). Removal from your list should require only sending an email and visiting a single web page.
5) Create both HTML and text versions of your message.
Many people read messages on their PDAs, which display HTML as garbage
6) Send images unless there is an option to view them on the Web or unblock them.
Many companies block images to protect employees and customers from pornography or other objectionable material. With images blocked, many of emails will be unintelligible.
7) Charge a fee to opt-out of your mailing list