You only have 3-4 seconds before someone decides whether they are going to open your email or not, so it is important to make an impact .. Best practices for subject lines are debatable, especially when different industries and topics Trying to compare. However, there are some ballpark best practices for subject lines that you can feel confident about following. Fifty letters is generally a good, safe rule of thumb to follow. However, people have seen great success with more than 70 characters and subject lines of less than 49, so hesitate to experiment. Other strategies that work well across subject lines include asking questions, counting lists, and personalization. The best email subject lines are specific, short, and compelling. Exceed expectations and leave email content to rest.