Almost half of all collection time at Royal Mail post boxes have been brought forward to as early as nine in the morning.
Post boxes are currently emptied at 4pm but the move will see them emptied between 9am and 3pm.
The changes affect 50,000 of the currently 115,000 post boxes national.
They are part of a restructuring process that will also see an additional 2,000 post boxes installed in rural areas and new developments.
The mail organisation has said it has made the move to safeguard the future of post boxes by making collections more efficient, in the face of declining letter and parcel volumes in post boxes.
The changes announced build on new safeguards for postal services in rural communities introduced last year by Ofcom.
This requires that 98 per cent of all households across the UK should be within half a mile of a postbox.
Mish Tullar, a spokesman for Royal Mail, said: “These changes will ensure it is sustainable for Royal Mail to maintain – and indeed increase – the number of post boxes in the UK.
“We already have a higher geographic density of postboxes than anywhere in the world, other than Japan. Not a single post box will be lost as a result of this initiative.”