Everybody's done it - hit 'Reply All' or added a whole group to an email list by mistake.
All you can do is watch as the tides of barely repressed fury and 'polite' requests to be removed from the thread are unleashed. All of whom have ironically also clicked 'Reply All'.
But today, according to NHS worker Olly Benson, this classic office gaffe occurred on a slightly bigger scale: an IT contractor who emailed the entire NHS.
The NHS employs around 1.2 million people. So you can imagine the apocalyptic effect of this fail on everybody's inbox.
The IT contractor at Croydon NHS was apparently sending a test email. Benson's latest update tells us that so far, he has received 187 "please unsubscribe me" emails. In three hours.
There have been claims that the entire email system has crashed, but according to NHS digital only 840,000 accounts were affected - although many users have experienced severe delays.
The Guardian has published the message that NHSmail users reportedly received, in which the faux pas was described as a "high severity service incident".
An issue with a distribution list has meant that several test emails have been widely received by users. This has been exacerbated by recipients replying in response and increasing the volume of emails associated with the list.
The impact of this issue has meant that some users are unable to access OWA [Outlook web access] due to the volume of emails being circulated.
According to a statement from a spokesperson to the Guardian, the distrubtion list has now been deleted so nobody else can 'reply all'.
As this Twitter user says...
Benson declined to comment on the incident.