Are you the type of person who always says thank-you? Well, if it's by email, you should stop, according to UK officials looking at ways to save the environment.
The Financial Times reports that we may all soon be encouraged to send one fewer email a day, cutting out "useless" one-line messages - such as "thanks".
Doing so "would save a lot of carbon", one official involved in next year's COP26 climate summit in Glasgow said.
But would it really make a huge difference?
Why do emails produce carbon at all?
Most people tend to think of the internet as a cloud that exists outside their computing hardware. But the reality is when you send an email - or anything else - it goes along a chain of energy-burning electronics.
Your wi-fi router sends the signal along wires to the local exchange - the green box on the street corner - and from there to a telecoms company, and from there to huge data centres operated by the tech giants. Each of those runs on electricity, and it all adds up.
But a single email's effect on such massive infrastructure is tiny.
Are my emails a big environmental problem?
The Financial Times report says the officials promoting this idea referred to a press release from renewable electricity firm Ovo Energy from one year ago.
It claimed that if every British person sent one fewer thank-you email a day, it would save 16,433 tonnes of carbon a year, equivalent to tens of thousands of flights to Europe.
The problem, however, is that even if the sums involved roughly worked out, it would still be a splash in the pond.
The UK's annual greenhouse gas emissions were 435.2 million tonnes in 2019 - so the amount in question here is about 0.0037% of the national picture. And that's if every single British person reduced their email output.
Mike Berners-Lee, a respected professor on the topic whose research was used in the Ovo Energy work, told the Financial Times it was based on "back-of-the-envelope" maths from 2010 - and while useful to start conversations, there were bigger questions.
On top of that, the estimate of how much carbon an email generates "takes into account absolutely everything involved", according to Chris Preist, professor of sustainability and computer systems at the University of Bristol.
It tries to include the energy used by servers, your home wi-fi, your laptop - even a very small share of the carbon emitted to construct the data centre buildings.
"The reality is that a lot of the system will still have impact, whether or not the email is sent," Prof Preist explains.
"Your laptop will still be on, your wi-fi will still be on, your home internet connection will still be on, the wider network will still use roughly the same amount of energy even with a reduction in volume.
"There will be a small saving in the data centre hosting the email, particularly if it allows them to use a few less servers. But the carbon saved will be far far less than 1g per email."
What can make a difference?
Rather than worrying about relatively low-impact emails, some researchers suggest we should turn our attention to services such as game and video-streaming and cloud storage which have a much larger effect.
But the topic is immensely complicated, and there is a debate about how estimates should be calculated - and who should be responsible for it.
Big tech firms such as Google, for example, are already proudly carbon-neutral: they pay subsidies for environmental projects to offset the carbon they burn providing your emails - and other services like YouTube.
"What really makes a difference is buying less kit, and keeping it for longer," Prof Preist explains. "But even this is small fry compared with your travel, heating your home, and what you eat."
He said consumers should focus their "eco-guilt" on things that make a difference - and not sweat the small stuff.
"That is the job of the companies providing the services, who should be designing their systems to deliver services in as energy and resource efficient way as possible."
His advice on email etiquette and thank-you messages?
"Send an email if you feel that the other person will value it, and don't if they won't," he said.
"The biggest 'waste' both from an environmental and personal point of view will be the use of time by both of you."
