The email contained an "important announcement" from St Kent's.
"Saint Kentigern College wishes to inform that all remaining scheduled performances of Sweeney Todd have been cancelled," the announcement said.
"If you are a ticket holder and have paid by credit card you will automatically be refunded by iTicket early next week.
"We sincerely apologise for any inconvenience this may cause. Naturally this is a trying time for the school, students, and their families, and this wasn't an easy decision to make.
"We hope you'll join us in sending your thoughts and support to all involved."
The company said all customers affected by the cancellations would be reimbursed in full early next week. Credit card payments would be returned automatically, and people who paid by other means would be contacted individually.
Two boys were taken to hospital on Wednesday, the performance's opening night, after their necks were cut with a real razor wrapped in duct tape which was used as a prop.
Both boys were discharged from hospital by yesterday afternoon, and school headmaster Steve Cole said he understood they were doing well.
However, he admitted the school was still in the dark as to how the incident could have occurred, saying the antique blade had been made safe.
The prop was a razor that had been blunted and wrapped in several protective layers, Mr Cole said.
"It's normal for Sweeney Todd to have such an instrument [and it] clearly had been checked many, many times," he said.
The unfortunate incident happened halfway through the second act, Mr Cole said.
The performance continued and audience members were unaware of the incident.
Yesterday Mr Cole said he hoped the rest of the shows in the run would be able to go ahead.
The school made the decision to cancel the shows late this afternoon.
Toi Whakaari drama school director Christian Penny told the Herald he did not think it was common for schools to use real weapons in their drama productions.
"I would be highly surprised [if they did]."
A real blade would almost never be used in a professional production at Toi Whakaari due to health and safety requirements, he said.
"This is training for the professional industry. Health and safety is right up there.
"It would be about making the effect work for the audience without putting anyone in any danger who is doing it."
Because school productions are run by teachers, who are busy and not trained professionals, health and safety standards are not necessarily enforced in the same way, he said.
"In a highschool you've got people doing the best with what they've got.
"I was surprised to hear they used a real razor - but I can see where they're coming from. They're trying to make it strong and effective, but you don't make it dangerous.
"It's an amateur culture and these kinds of accidents can happen. It's not good, but it can happen. In a professional setting if it happened - well, we train people to make it not happen."
Yesterday St Kentigern's head of college, Steve Cole, said the year 12 and 13 students in the performance had wanted everything to be "as authentic as possible" including using real blades, which he said had been blunted and wrapped in protective layers.
The throat-cutting scenes had been rehearsed dozens of times in the months leading up to the performance's opening night without incident, Mr Cole said.
