There may be thousands of different ways to become a millionaire, but don't think that means that hugely successful people are as wildly different as the paths they took to riches. According to a host of experts, while the world's richest people may have rose in different industries and using different business strategies, most have a few fundamental traits in common.

What are these habits and behaviors? We've covered plenty of them here on before, but one quirk of the millionaire approach to life has remained unexplored -- how they manage email.

If you think your inbox overload is bad, imagine the number of messages millionaires have to cope with. But according to author Kevin Kruse, despite what must be an insane volume of email, the super successful don't get stressed out about their inboxes (and this isn't all down to an army of assistants processing incoming mail).

As part of his research for his new book, 15 Secrets Successful People Know About Time Management, Kruse interviewed more than 200 millionaires and discovered that they take a remarkably consistent approach to email. In a recent Medium post, he boils down the email wisdom of millionaires into five essential principles. Here are the basics:

1. No more newsletters

"Do you really need to subscribe to all those flash deal-of-the-day offers? Those viral clickbait 'news' headlines? Don't give companies permission to intrude on your day," writes Kruse. If you want to email like a millionaire, he suggests you head over to and axe as many subscriptions as possible. And if you really need to keep a few, "use a secondary email address for them, and schedule time off-hours to read them all at once," he recommends.

2. Turn off notifications

If you need to reach someone really urgently, you call them. Therefore, email, by definition, can always wait a while. That's why millionaires have no time for chiming notifications. Kruse offers strong language on the subject: "Getting email notifications is a sin. Notifications interrupt your concentration, your work sprints, and your ability to be present and mindful during meetings and conversations. Whether you have an audible ding, a phone vibration, or a little window that pops up with every new email - turn it off."

3. Think before you forward or CC

A key step to controlling what comes into your inbox is being more thoughtful about what goes out. Millionaires know this simple truth: "If you send less email, you'll also receive less email."

4. Keep it super short

You might have heard of Jeff Bezos' infamous question mark only emails. He's not the only super successful person who believes in extreme brevity when it comes to composing messages. Here's what Hootsuite CEO Ryan Holmes told Kruse: "Keep emails short and sweet. Over the years, I've trained myself to write three-sentence emails, leaving out the fluff and keeping only the most essential points. It saves my time and it saves the reader's time."

5. Process email with 'the four Ds'

Every time you open an email ask yourself, 'Should I delete this, delegate it, do something about it in five minutes or less, or defer it for later?'

The essential point of this exercise is to keep email from repeatedly sidetracking your day. If a message is going to take more than a few minutes to respond to, don't interrupt your concentration to answer it right then and there. "Ultra-productive people don't respond to email through constant check-ins," insists Kruse. Instead, they schedule a few short blocks of time to devote to processing email each day.