But instead the staffer attached a spreadsheet with the name, address, email, parking space location and amount paid for it for 549 clients.
At 12.03pm he issued an email recalling the previous message, and at 12.35pm the correct email was resent.
The client who contacted the Herald said the blunder was unacceptable. "I'm not overly concerned about my details being out there, but I'm annoyed," he said.
Auckland Transport chief executive David Warburton was confident the error was "an isolated incident rather than a systemic problem" with how the agency handled personal information.
"Auckland Transport unreservedly apologises for accidentally emailing a list of leaseholders ... as a result of human error."
He confirmed Auckland Transport had sent a further email last night "to all affected leaseholders" apologising and asking them to delete the spreadsheet sent in error.
"Auckland Transport has also contacted the Privacy Commissioner to advise of the breach," he said.
It is understood the staffer responsible for the botched email alerted Auckland Transport management immediately. It was unlikely the person would face any internal action as the incident was seen as an "unfortunate mistake".
But Auckland Transport was investigating and would make any changes necessary to prevent similar incidents.
The apology email was sent at 5.21pm, from Auckland Transport's parking services manager, Liz Hogan.
"If you have particular concerns regarding this I would urge you to contact me directly," she said at the end of her email.
The gaffe comes after Auckland Transport mistakenly referred more than 200 motorists to a debt collector for unpaid parking fines in February.
The agency was forced to send 237 apology letters to motorists explaining why their details had been sent to Baycorp prematurely.
The motorists had been ticketed but Auckland Transport did not send out infringement payment reminder notices. A "systems error" led to the unpaid tickets being referred.
