E-mail marketing is one of the strongest tools for affiliates. Affiliates utilize e-mail marketing to promote multiple affiliate programs in a targeted newsletter, or they build an opt-in email list for a targeted niche and send out solo e-mail to the list.
It is essential to adhere to the CAN-SPAM law. Be sure to educate yourself on the requirements before sending out e-mail.
Here are some of the more popular services (and the two I personally use) for gathering opt-in e-mail addresses and sending e-mail:
