When planning your marketing mix, the most important component is email. Why? Because its the easiest way to reach people, considering that 85 percent of the world and 91 percent of the US have an email address and check their inboxes daily. Its also the digital marketing workhorse that generates the highest ROI, outperforming social media and even direct mail! If you're trying to be hip, sure, you can fire up an Instagram or Snapchat account. However, if you're actually trying to make some money, turn to good ol reliable email.

You probably have a bunch of questions on how to jump-start an email campaign. When should I email people? How do I build my list? How can I do this efficiently? After reviewing thousands of email campaigns as the CEO of an email marketing company, I've come up with these six indispensable rules for building a killer email program. They will help you to maximize subscriber rates, engagement, and ROI across your campaigns.

Once upon a time I worked on the growth engineering team at Twitter. We were tasked with building something that could turn new signup users into die-hard Tweeters. The secret sauce to user activation was email! But before we knew when to use email, we had to map out the Twitter user journey.

Looking closer into the data, we noticed that Twitter users became long-term loyalists when they achieved a certain number of mutual follows. As a result, we developed a series of emails that would encourage users to find their friends on Twitter and suggested other users to follow. The email below was sent every 4-7 days to a user until they hit the critical number of mutual follows.

I advise every company to start by creating a map, because without understanding how your users interact with your product or website, you really have no idea how to communicate with them using email. As you learn more about your users, continuously make the map more detailed until you find that inflection point or points. Once you uncover the sweet spot, use email as your secret weapon to push users towards that inflection point, whether its becoming a core user or a recurring customer.