NHS IT systems were brought to a halt after a Croydon-based "senior ICT delivery facilitator" accidentally added all almost one million staff members to a mailing list and sent them a test email.
Disgruntled staff hitting 'Reply to all' to request being removed from the list, together with additional 'read receipt' requests, consequently caused many internal communications systems to slow to a snail's pace.
The NHS admitted that as many as 840,000 staff were subsequently locked out of NHSmail, the organisation's in-house email service. Outgoing and incoming emails were delayed by as much as three hours as a result. The distribution list has since been removed.
NHSmail runs on Microsoft Exchange. The IT organisation admitted the error in a service status update this morning, and has disabled the dynamic distribution list feature as a precaution.
"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," said the update.
"The impact of this issue has meant that some users are unable to access Outlook Web Access due to the volume of emails being circulated. The distribution list has been removed and associated emails are being traced and cleared."
Part of the problem, according to insiders, was not simply the size of the distribution list, but the inclusion of other lists that multiplied the effect, especially for staff already on multiple email distribution lists.
It has also been suggested that NHSmail is bad enough at the best times, and that routine emails typically take at least an hour, and sometimes days, to arrive.
The email was supposed to be part of a distribution list entitled CroydonPractices, and therefore presumably intended only for GP practices in Croydon, indicating a pretty major cock-up on the part of the senior ICT delivery facilitator fingered for the error.
Staff, naturally enough, took to social media to vent their frustration at the situation.
... so latest is 187 "please unsubscribe me" emails while I've been in meetings.— Olly Benson (@ollybenson) November 14, 2016
i thought i was bad with technology but at least i've never managed to email the entire nhs in one go— lily (@Iilypxtter) November 14, 2016
Oh dear- someone seems to have sent an email to the entire NHS address book- cue lots of reply all emails asking why they've been included 🙄— Ali Aslam (@aaslam) November 14, 2016
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