The widely publicised reply-all email error from last year involved 500 million emails being distributed across the health service network in total.
This vast email payload was sent out in just 75 minutes, according to an investigation into the matter.
What began with an innocent test message quickly turned into a system-destroying problem.
A senior associate ICT delivery facilitator had believed that she was sending an email to a local distribution list, but instead sent it to 850,000 NHS workers.
The blank message, sent early in the morning with a subject line that simply read “test”, was sent to a distribution list called “CroydonPractices”.
This prompted an angry response from some individuals who shouldn’t have received the message, and this is when the chaos began.
“NHSmail’s Dynamic Distribution List (DDL) functionality allows administrators to create distribution lists using a range of options and rules,” an official report into the meltdown stated.
The new information is contained in papers to be submitted to the NHS digital board by James Hawkins, NHS Digital’s director of programmes.
NHS Digital’s chief operating officer, Rob Shaw, has approved the paper.
“A software configuration error meant that the system applied an ‘All England’ rule rather than one including only the administrator’s organisation. The administrator would not have known that this had occurred,” continued the report on the issue.
Emails were delayed by up to three hours at the time, with half a billion emails being distributed the NHS network between 08:30 and 09:45.
Nonetheless, the service remained pretty steady, and the report claims that it didn’t actually crash any stage, even though serious delays were experienced.
The NHS report is extremely critical of outsourcer Accenture for failing to build in adequate failsafes.
One of the NHSmail system’s design requirements was that “strict controls must be in place to limit the volume of any one email sent by an individual user or local administrator,” the report notes.
“This functionality is still to be delivered by Accenture. The ability to create DDLs of similar form will remain disabled until NHS Digital is satisfied this has been delivered,” the report concludes.