The 5 Magic Elements That Boost Email Marketing ROI Into the Stratosphere Email seems so old school, but when you get the essentials right it sizzles.

For every $1 businesses spend on email marketing they generate about $40 in ROI, according to Mike May of MediaPost's Email Insider. Although email seems unappealing compared with social media and emerging trends like native advertising, email consistently proves to be the most engaging medium for marketers.

Whether you are new to email marketing or are a seasoned guru, here is a quick checklist of five essentials for your overall email strategy:

1. Powerful subject lines.

To get your foot in the door, recipients first need to open your email. In 2013, business email accounted for over 100 billion messages sent and received per day. With a mediocre subject line, your cold outreach email, newsletter or sales pitch will get lost in all the noise.

Not to fret. Here are three tips for crafting compelling subject lines from Copyblogger's Brian Clark:

1. Make it useful, ultra-specific, unique and urgent.
2. Identify yourself, leverage spam checking tools and keep it short.
3. Establish trust and rapport with recipients on your list.

Over time, email will become your most important asset as other marketing channels wax and wane in ROI.

Related: Should ROI Be Attached to Every Marketing Activity?

2. Empathy toward customer intent.

Understand where your customer is in the sales cycle. Are they still exploring their options? Do they need more information about your company and industry? Are they ready to buy?

Untargeted email blasts are doomed to fail. Develop a number of emails that nurture leads and help readers progress through the sales funnel. Segment your users and set automatic triggers to send the best emails to the right contacts at the perfect time.

3. Compelling images.

The right visual assets make your message pop and encourage recipients to read an email in its entirety. The wrong image might send your newsletter straight to spam.

Azure Collier, social media education developer for Constant Contact, recommends that brands keep their emails short and quick. High-definition visuals can lead to slower load times, which may cause less patient customers to abandon your email before it fully loads.

To create awesome visual content for your next email blast, use Canva, PlaceIt or The Noun Project.

Related: The 5 Mistakes That Will Land Your Email in the Spam Folder

4. Compelling calls to action.

Your customers need direction. Even after they open and read your email, their engagement may provide little or no ROI if you are not actively encouraging contacts to take a specific action.

To create the perfect call to action, Alexis Rodrigo of Vero shares four tips:

1. Include copy that is low risk, high reward. Offers should be less intimidating and more inviting.
2. Place your CTA at the bottom of your email, preferably on the left hand side.
3. Add subtle elements to your buttons to make them pop, including graphic elements like an arrow.
4. Include multiple CTAs in different formats (button, graphic, plain text, etc).

Including strong CTAs in every email you send will help you achieve all of your marketing goals faster.

5. Mobile optimization.

Mobile devices are taking over the world. According to a report by Litmus, 53 percent of emails are opened on smartphones and tablets. With a majority of emails being read on-the-go, marketers ought to carefully design their emails to be mobile responsive.

Consumers easily spend more time staring at their phones than at the TV. They are practically glued to their devices. The adoption of mobile has led to an on-demand society filled with people who have increasingly short attention spans. Marketing emails need to fully optimized for the mobile viewing experience if businesses expect recipients will read, enjoy and forward those emails to friends.

Related: 7 Tips to Make Your Email Marketing More Mobile-Friendly