In this day and age, it's harder than ever before to disconnect from work.

Once a person has signed off for the day, they might feel pressured to reply to an after-hours email that pops up on their phone, even if it's not urgent.

A new psychology study by researchers from the London Business School in the UK and Cornell University in the US has identified simple email etiquette that sets healthier work/life boundaries and relieves some of the stress of having to be 'always on'.

All that's required is a single sentence tacked onto the end of an after-hours email that goes something like this: "This is not an urgent matter, so you can get to it whenever you can."

Seriously, that's it. And while you might think the message goes unsaid, it doesn't.

The findings come specifically from a study that included 852 full-time employees in the United States who were randomly split into two groups: the hypothetical email sender and the hypothetical email receiver.

In the experiment, researchers asked senders how quickly they expected whoever was receiving their email to respond, while receivers explained how quickly they felt they needed to reply.

The findings reveal a breakdown in communication, which leads to what the authors have called "the email urgency bias".

While email senders often do not expect a quick reply when they shoot off an after-hours request, email receivers tend not to 'get' that message. Instead, they often default to thinking all emails require a rapid response, a stressful state of mind to be sure.

The good news is that when an email sender explicitly states that an urgent reply isn't required, the email urgency bias and its ensuing stress appear to be alleviated.

"From a practical perspective, our research can help mitigate the spread of unhealthy work cultures where employees feel pressured to stay connected to their work even when they are not expected to do so," the authors of the study write.

"Given that email continues to be one of the primary modes of workplace communication and among the most widespread online activities, our goal for limiting its negative impact should not necessarily be less email, but rather better email."

The authors based their recommendations on a series of psychological experiments conducted among six different cohorts.

The first study included more than 700 public sector employees living in Spain who rated how happy they were with their current work/life balance. They then wrote down their experience with either receiving or sending emails outside of their regular work hours.

Specifically, researchers wanted to know, on a sliding scale, how quickly participants expected someone else to reply to their email or how important it was that they answer someone else's in the real world.

Like with the US group, the findings found a mismatch in expectations between the sender and the receiver. Often, the sender didn't expect an urgent response, while the receiver tended to think they needed to reply right away.

Those employees more prone to this 'email urgency bias' scored lower on subjective wellbeing.

The second study explored the possible stress of high expectations, this time among 251 participants, who were also split into hypothetical email receivers and hypothetical email senders.

The email receiver was asked to imagine that they'd just arrived home from work and checked their email to find a non-urgent message from their colleague. The email senders were asked to imagine the reverse scenario: They knew their colleague had already gone home but that they had a question at the end of the day.

Both groups were then asked how quickly a response was expected. Once again, the authors found receivers assumed they needed to respond more quickly than senders expected.

The third study included over 600 participants and found that urgent and non-urgent emails sent after hours are treated relatively the same way. A fourth study with 411 participants confirmed that emails sent during work hours and emails sent after work hours are treated similarly, too.

In other words, all work emails, regardless of when they're sent and how urgent they actually are, seem to be urgent to us. That urgency is not necessarily good for our health, especially when it seeps into our off hours.

A fifth study with 450 participants suggested response speed expectations for emails can add stress to a person's life, lowering their overall wellbeing. In fact, emails sent after work hours, even if they aren't urgent, seem to cause more stress to the receiver than when they are actually working.

The final and sixth study was the culmination of all these pursuits. It confirmed the idea that emails sent after we've clocked off can add stress to our lives by making us feel as though we need to reply straight away.

It also suggested an email sender can reduce the stress of their colleagues by being very explicit about what they want and when they want it in an after-hours email.

"Namely," the authors conclude, "we found that senders can help receivers feel less pressure to respond right away to non-urgent work emails sent off-hours simply by making their expectations of response speed explicit through a note in their email that specifically states they do not expect a response right away."

Seems like a simple fix.

The study was published in Organizational Behavior and Human Decision Processes.