A work email should be no longer than a text message.
If you use it as anything other than a "quick messaging system", you can easily waste countless hours every week participating in lengthy email exchanges, according to C.L. Max Nikias, president of the University of Southern California, news.com.au reports.
Writing in The Wall Street Journal, Mr Nikias explains how he has used this technique to reduce the time spent on his emails from about half of his waking day to an average of just two hours - far less than the "startling" 7.4 hours of the average professional.
"I receive over 300 emails every day," he writes.
"Rather than spending my time glued to a screen and responding endlessly, I keep all of my emails brief - no more than an average text message.
"I am now certain that any topic that requires further deliberation is more effectively and more efficiently hashed out by phone or in a face-to-face meeting rather than in a rambling series of lengthy email exchanges."
Over his career, Mr Nikias says he has come to appreciate an "overriding principle".
"Effective leaders must maximise efficiency and speed on some tasks, in order to devote thoughtful focus to others," he writes.
"Email can throw a leader off course if used as anything more than a quick messaging system. After all, the leader has to keep the big picture in mind, and therefore must avoid being redirected constantly by other's agendas."
He says the "text message" rule has made him more productive while allowing him to be properly briefed on the most important priorities. "For example, USC a few weeks ago completed the largest campus expansion in our history," he writes.
"While I visited the site regularly, our capital construction managers would also update me by email with designs and photos of everything from brick samples to stained glass windows, with brief summaries of the development's progress.
"I offered approvals and requests for simple changes in text-sized emails. However, if there was an issue that required further deliberation, I would initiate a phone call that rendered further emails moot."
For anything more complicated, he argues nothing beats face-to-face communication. "I meet with all of my direct reports as a group, each week to discuss every important decision point the organisation is facing," he writes.
"Unlike my brief emails, these meetings take more than half the business day, and I expect in-depth discussions that allow my senior officers to weigh in on issues both within and outside of their regular portfolios of responsibility.
"It is there that the most important decisions are made and the most important principles are laid out for our organisation. And it is the reliable, weekly timing of these longer face-to-face discussions that allow us to keep our email usage to a minimum."
In 2015, Australian advertising agency Atomic 212 announced it was banning internal emails entirely in an attempt to "bring energy back to office" through face-to-face and phone conversations.
"In the old world if I was going to ask you to assist with something like writing a report, I'd walk up to you and talk to you, look you in the eye, and that would engender empathy," Atomic 212 chief executive Jason Dooris said at the time. "When you flick an email you lose that connection."