A common question that I get asked is "I want to do an e-mail campaign, but how do I stay out of the spam filters?". You can avoid the spam folder by following the CAN-SPAM law, keeping your list clean and writing content that can't be considered spam. A couple of examples of what would be considered spam: using all caps or writing a "sales" pitch right out the "gate" with the words "free" written throughout the e-mail.
Save yourself a lot of headaches - Make sure your list is DOUBLE opt-in! Sending a confirmation e-mail after they sign up will ensure they want to receive information from you. Once they've confirmed, send an e-mail right away. We all get busy and have a tendency to send e-mails 2 - 3 weeks after people signed up; there's a good chance they won't remember you and hit the delete key - keep yourself in front of them! Now that you have your list confirmed, keep it clean.