A successful email should have a compelling subject line, engaging content, and a clear call-to-action (CTA). The subject line is the first thing recipients see, so it should be attention-grabbing and relevant. The content should provide value to the reader, whether it's informative, entertaining, or offers a solution to a problem. Finally, the CTA should be clear and encourage the recipient to take the desired action, such as clicking a link or making a purchase.