A reply-all email thread is like a very loud, very annoying megaphone. Do not shout into it. Christopher Furlong/Getty Images The NHS's 1.2 million employees are currently trapped in a "reply-all" email hell.

A "test" email was accidentally sent to everyone who works at the UK health service — prompting a series of reply-all responses from annoyed recipients going out to all 1-million-plus employees of the organisations.

An NHS employee told Business Insider that there have been at least 120 replies so far — meaning that more than 140 million needless emails have been sent across the NHS's network today. As a result, they said, its email systems are running "very slow today."

The NHS Pensions department is currently warning people on Twitter that "if contacting us by email please be aware that there may be delays in responding due to an issue currently affecting all NHS mail."

Here's a reminder of what to do if you're caught up in a reply-all email chain: Nothing.

Do not reply asking people to stop emailing. Do not ask what's going on. Do not ask to be removed from the mailing list. Do nothing.

Anything else is counter-productive — so just sit back, ignore it, and trust everyone else to do the same. Good luck.