How would you describe an effective leader?

There are many ways to answer that question, but most would agree that true leadership involves the ability to practice what one preaches, to set the example, and to inspire others.

Over the past few years, I've studied the leadership styles of numerous successful business leaders while researching my forthcoming book, EQ, Applied: The Real World Guide to Emotional Intelligence. One lesson that stood out is the powerful way email is used--yes, email--to quickly communicate vital lessons at the right time.

Below, you'll find excerpts of three extraordinary emails from the chief executives of Microsoft, Starbucks, and Amazon, and the brilliant lessons we learn from each.

Microsoft's Satya Nadella encourages employees after an epic fail.

About a year ago, Microsoft launched a Twitter bot by the name of Tay (officially, Tay.ai), in an attempt to advance artificial intelligence communication. Things went desperately wrong, though, when hackers and others caused Tay to begin spewing racist and profane comments--prompting Microsoft to shut down Tay just a few hours later and apologize.

No doubt, the "Tay team" must have felt extremely down after this debacle. So you can imagine their response when they received an email from their CEO that included the following statements:

"Keep pushing, and know that I am with you ... (The) key is to keep learning and improving."

Takeaways: People need to know you've got their back. We all make mistakes. The question is, how can you help your people recover from those failures?

In an interview, Nadella went on to explain the reasoning behind his encouraging tone:

"It's so critical for leaders not to freak people out, but to give them air cover to solve the real problem. If people are doing things out of fear, it's hard or impossible to actually drive any innovation."

When you encourage and build others up, rather than dishearten and tear down, they'll be motivated to continue giving their best.

Starbucks's Howard Schultz inspires employees after stock market chaos.

In Aug 2015, signs of an economic slowdown in China triggered panic and resulted in more than $1 trillion being wiped from Asian markets, sending the Dow plunging 588 points in a single day and prompting the trending hashtag: #GreatFallOfChina.

Starbucks's chief executive (at the time), Howard Schultz, wanted to make sure Starbucks employees were well aware of the situation--all 190,000 of them. So, he sent a compelling memo encouraging them to show special consideration for consumers:

Our customers are likely to experience an increased level of anxiety and concern. Please recognize this and--as you always have--remember that our success is not an entitlement, but something we need to earn, every day. Let's be very sensitive to the pressures our customers may be feeling, and do everything we can to individually and collectively exceed their expectations. ...The experience we deliver in our stores, the strength and equity of our brand, and the primary reason for our current and future success is because of all of YOU. I believe in you and have never been prouder to be your partner.

Takeaways: Leadership and culture start at the top. It would have been easy for Schultz to read the news and move on, neglecting the opportunity to have any type of impact on his employees. But Schultz took advantage of a great opportunity to exert positive influence--in this case, inspiring his people to improve their customer service on what would certainly be a depressing day for many.

Schultz managed to do this, not in a manner that was condescending or demeaning, but rather while dignifying and praising his people at the same time.

Jeff Bezos uses a New York Times exposé to make Amazon better.

In the summer of 2015, The New York Times published a scathing piece portraying Amazon, the world's largest retailer, as a brutal employer that puts innovation and company performance above its' people's well-being.

I'm sure Bezos felt the criticism was unduly biased. ("I don't recognize this Amazon, and I very much hope you don't either," Bezos told employees.) But through an internal memo, Amazon's chief nevertheless encouraged his people to read the Times piece, and to "escalate to HR" any stories they knew of like those reported--even inviting individuals to email him directly. (Interestingly, Amazon later revealed significant changes to the way it would assess employees moving forward.)

Takeaways: Bezos's initial response demonstrated a remarkable ability to set emotions aside and learn from criticism--even if it's not delivered in an ideal way.

Criticism is never easy to take, but it can help us discover blind spots and find areas for improvement. And even in those cases where negative feedback is completely unfounded, it still provides the opportunity to see things from another perspective--which can lead to invaluable insights.