Know your spam rules. A lot of innocent people send spam because they didn't know any better. Read up on the CAN-SPAM act to avoid any trouble. Put simply, you're allowed to send bulk email only to people who specifically asked to be on your mailing list. If you collected email addresses for a lunch giveaway or an event invitation, then you don't have permission to send marketing emails unless you made that clear at signup. Include an obvious unsubscribe link in every email, and don't forget to remind subscribers how they got on your list in the first place.
Give people a way to avoid more emails about the same offer. If you do a concentrated promotion for something, you might send lots of emails about it in a short time. Give people the option to avoid future emails about the offer. Just add a link to the end of the emails (e.g., “If you’re sure you’re not interested in [ offer ], click here, and I won’t send you any more emails about it this year.”). That way you won’t annoy people who aren’t interested in the offer now. You could argue that some of them might buy if they saw all the emails. Well, if you’re only interested in this month’s sales, send as many emails as you can. I just assume you want to have someone left on your list for next month.
You split your email subscriber list into “cold” vs. “warm” leads so you can compare similar groups of customers in this test. You prepare two versions of your email—one with the normal subject line, and one with a much shorter, punchier subject line. You send half of your cold leads the normal subject line and half of your cold leads get the new, exciting subject line. You also send half of your warm leads the normal subject line, and the other half get the new subject line.