Royal Mail cut nearly 6,500 post box collections last year, figures have revealed.
The postal service also brought forward final collection times at more than 4,000 post boxes, meaning customers have to post their letters earlier.
In the 12 months to March 2012 Royal Mail cut 9,689 collections from some post boxes, while adding 3,236 at others - leaving a net loss of 6,453 collections.
Figures also show the final collection times for 10,006 mail boxes were brought forward, while the times were extended for 5,719.
Heulyn Gwyn Davies, a spokesman for Royal Mail, said: "This is sensible ongoing business management which simply reflects changing mail volumes in specific locations."
He said the number of post boxes in the Royal Mail network has increased by 48 over the last three years to 115,271 despite a decrease in mail volume, and added that the postal service makes 270,000 collections a day.
The collection figures are not published as a matter of routine, but were disclosed after a Freedom of Information request by shadow postal affairs minister Ian Murray.
Royal Mail has defended the cuts, saying that it was adjusting the frequency and times of collections at its post boxes to suit the demand and to save money.
Mr Davies said: "Royal Mail is committed to maintaining one of the highest quality postal services in Europe. We collect and deliver six days a week, often more than once a day, while the EU Directive only requires us to collect once a day, five days a week."
The company has to stick to strict final collection times for each post box under an agreement with postal regulator Ofcom, Mr Davies said.
"There are strictly limited windows for final collection times agreed with Ofcom designated for every post box, whether urban, suburban or rural.
"From time to time, as a matter of good business practice, we make adjustments to the final collection times within the allowed windows, or the number of collections per day. We may plan earlier collection times for low volume boxes and later collection times for high volume boxes.
"This process can involve either extending or bringing forward collection times. It can also mean adding or reducing collections.
"We notify both Ofcom and Consumer Focus well in advance of any proposed changes to collection times for individual post boxes. We also want to be as clear as we can with local residents where changes are proposed.
"So, we publish an information notice at least two weeks in advance on each post box concerned, with a contact number for customers to ring if they wish more information and details of the collection times of other post boxes nearby."
Robert Hammond, director of postal policy at Consumer Focus said: "Consumers need convenient access to a post box and that is why there are strict Ofcom rules about how many post boxes an area should have, based on population density.
"Against a backdrop of rapidly declining mail volumes the closure of some post boxes is understandable. However, customers must be made aware of these changes and there must be an alternative post box nearby. Post box closures or changing collection times should not result in problems with access or a lower quality of service for customers. This is something that we will be discussing with Royal Mail."