A group test email that was accidently sent to more than 840,000 NHS staff has brought the entire system across the UK to a grinding halt.

A “bug” in the new NHSmail 2 service resulted in one unfortunate NHS IT contractor sending her test email to every NHS mail account in England this morning.

The resulting flood of “reply all” emails was too much for the email system with more 1.2 million users across the UK, with staff across the NHS not receiving any emails for hours. Some staff said they received as many as 300 reply all emails, which would eqaute to an extra 250 million emails sent across the system.

NHS staff took to social media to vent their fustration, presumably unable to use email without exacerbating the problem further.

The hashtag #NHSmail and ReplyAllGate were trending on Twitter on Monday afternoon, with comments ranging from suggesting the entire epsiode was designed to root out staff that required further IT training to pleading with people to stop hitting 'reply-all' to the errant missive.

"Every time you hit 'reply all' you're helping generate another 840k emails to the #nhsmail server! Stop!" one user tweeted.

An NHS Digital spokeswoman said the NHS mail had not shut down completely but, because of an email “inadvertently added everyone on the NHS mail list”, some email accounts “were operating slower than normal”.

The distribution list had been removed this morning but delays were continuing into the early afternoon on Monday as the traffic volume remained high.

“Anytime they hit ‘reply all’ that goes out 840,000 times.”

The service status on NHS Digital’s website states:

“An issue with a distribution list has meant that several test emails have been widely recieved 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 due to the volume of emails being circulated.”

The NHS Digital spokeswoman said the staff member who sent the email was not to blame and the expansive distribution list was instead the result of a “bug in the system” provided by NHSmail supplier, Accenture.

“It was not her fault.”

NHSmail 2 was rolled out earlier this year, since it became clear its ageing predecessor could not cope with the growing demand.

Vodafone had been the incumbent provider of the NHSmail service after taking over Cable and Wireless, which has been the supplier for NHSmail since its launch in 2002, initially using the Mirapoint platform but moving onto Microsoft Exchange 2007 in 2009.

In June last year the Department of Health announced that consultancy firm Accenture was the winner of the £60 million contract to provide the new NHSmail service, which covers NHS organisations in Scotland and England, beating competition from BT. 

Accenture refused to comment on the outage, referring all questions to NHS Digital.