The virtual shutdown of NHSmail system caused by an inadvertent group email to nearly a million people has eased, although some users could still experience “minor delivery delays”.

NHS Digital updated its NHSmail service status page on Tuesday afternoon to indicate that the service, which has more than 1.2 million users, was returning to normal.

“Message queues on the email gateway have now cleared down to residual volumes and emails are processing through the platform successfully.”

However, the severe incident remains open as of 4.30pm and users were warned external inbound emails could still experience delays. Some of these delays were the result of "users deleting unwanted emails received yesterday and the early hours of this morning".

Some users have reported still not being able to access their inbox on Tuesday.

On Monday, a Croydon-based IT consultant accidently sent a test to all 840,000 NHSmail accounts in England.

The subsequent rush of ‘reply-all’ email, often sent by people requesting removal from the email group, brought the entire NHSmail service to a grinding halt.

People were unable to access their flooded inboxes and experienced hours in delays. Some people reported receiving more than 300 reply-all emails, which across the system would equate to more than 250 million extra emails.

On Tuesday, the consultant's employer, the South East Commissioning Support Unit, apologised for any disruption caused the NHSmail users but stressed a fault, not the individual, was to blame.

"We are supporting our staff member who has unfairly been the subject of numerous social media posts and media stories," the CSU said in a statement.

Both #NHSmail and #ReplyallGate were trending nationwide on Twitter on Monday, as people pleaded with their colleagues to stop hitting ‘reply-all’ and exacerbating the delays further.

NHS Digital has said the unfortunate IT consultant was not to blame for the erroneously broad distribution list, which was the result of a bug in the supplier’s system.

The distribution list was shut down by 10am on Monday, preventing any further ‘reply-alls’, although on social media NHSmail users were reporting delays well into Monday afternoon.

Accenture is the supplier of the NHSmail system but has refused to comment, referring all questions to NHS Digital.

NHSmail underwent a major revamp earlier this year, known as NHSmail 2, migrating off an ageing system that had been in use since 2002. At the time, NHS Digital called it one of the biggest mass inbox migrations in history.

However, the shift has not been with complaints. Last month, Digital Health News reported that complaints about NHSmail had more than tripled since the move to NHSmail2.