There are some 85,000 post pillar, wall and lamp boxes across England, and around 115,300 across the UK as a whole - with some of them listed as protected heritage for their historic importance and unique features.
Under the new policy, Royal Mail has pledged to manage, repair and conserve its network of post boxes in their existing locations and has set out how the organisation works to prevent illegal damage or theft of the boxes.
The new commitments update the original policy from 2002 to recognise changes in legislation and allow for recent developments, such as painting 110 post boxes gold to celebrate London 2012 British Olympic and Paralympic champions.
And it renews Historic England’s commitment to work with Royal Mail using heritage protection measures to ensure post boxes are kept and well cared for wherever possible, the organisations said.
The agreement will be adapted to reflect the individualities of post boxes around the UK, Royal Mail said, with equivalent policies with heritage agencies in Scotland, Wales and Northern Ireland.
Sue Whalley, Royal Mail’s chief operating officer, said: “There are around 115,300 pillar, wall and lamp boxes nationwide and there is a post box within half a mile of over 98% of the population.
“Some post boxes are rarer than others and some have a very special place in our heritage. They are also an icon of the UK’s postal system around the world.
“We are proud of our much-loved post boxes and go to great lengths to maintain and repair them.”
She said the policy would help ensure the preservation of all post boxes for future generations.
Duncan Wilson, chief executive of Historic England, said: “Post boxes are a cherished feature of British streets, adding character, colour and historic depth.
“Around 200 of the oldest and most rare are listed, but all are important to our heritage.
“We are happy to have signed this agreement with Royal Mail which seeks innovative ways to respond to crime prevention and ensures the care and retention of our world-famous heritage.”
Post box: factfile
The roadside post box was introduced in Britain following the 1840 postal reform which provided for universal affordable postage.
The idea of a locked roadside box and regular collection times was adopted from the continent by novelist and General Post Office official Anthony Trollope.
The first free-standing post boxes were installed in the Channel Islands in 1852 and in mainland Britain in 1853.
Unusual examples of the post box range from a Victorian wall box built into an edifice resembling a wayside shrine, to a 1930s “K4 Vermillion Giant” which combines a telephone kiosk, stamp vending machine and post box.