Collection times at almost half of Royal Mail's postboxes are to be brought forward to between 9am and 3pm.
The organisation says between 45,000 and 50,000 of its 115,300 postboxes will be affected by the change, which Royal Mail claims will better reflect user needs and unlock potential efficiency savings.
There will still be a late posting box within half a mile of each postbox that moves to earlier collections.
According to Royal Mail, many postboxes no longer cover their costs as a result of the declining popularity of letters. The new 'Collection on delivery' arrangements are being introduced as an alternative to decommissioning unprofitable boxes.
'Collection on delivery', which involves the picking up of mail by the local postman or woman on their delivery route, is already practised in many rural areas.
Royal Mail is to open 2,000 new postboxes, most of which will be in rural locations, particularly in Scotland and Northern Ireland.