A water firm has paid £60,000 compensation to customers after it found almost 4,000 unread e-mails dating back seven years.
Thames Water said the messages were sent to the e-mail address starting 'customerfeedback' rather than the correct 'customer.feedback' address.
The company only noticed the error in March and has paid compensation to the customers it could identify.
The blunder came to light in a report from water regulator Ofwat.
The water firm, which supplies the Thames Valley and London, alerted Ofwat after the unread messages were found.
A spokesman said: "As soon as we found the error we told Ofwat and put our hands up straightaway.
"The messages should have bounced back when customers missed out the dot but they somehow ended up in an inbox we were not aware of.
"We are sorry for the error but putting it into context we get 3,000 contacts from customers every day and this is over seven years."
He added that 1,200 customers had received £40 compensation and 600 had been given £20 each.
Water companies are subject to a statutory requirements under which they must pay £20 compensation if they fail to respond to complaints or account inquiries within 10 working days.
For complaints, if the firm has failed to pay 10 working days after the payment was due they are bound to make an additional payment.
Ofwat said the company's approach to tackling the issue had been positive.
It added: "Thames [Water] has taken action to address the root causes of the failure and has put in place measures to prevent it being repeated."
The report did contain better news for the water company, showing it had met targets to reduce leaks for the fourth year in a row.