You have only 3-4 seconds before someone decides whether or not they are going to open your email, so it's important to make an impact.. Best practices for subject lines are debatable, especially when trying to compare different industries and topics. However, there are some ballpark best practices for subject lines that you can feel confident about following.

Fifty characters is generally a good, safe rule of thumb to follow. However, people have seen great success with subject lines over 70 characters and less than 49, so feel free to experiment. Other tactics that work well in subject lines include asking questions, numbered lists and personalization.

The best email subject lines tend to be specific, short and compelling. Set expectations up front and let the email content do the rest.