A new fleet of mobile post offices will provide "walk-in" services in 250 rural areas every week.
The 40 "post offices on wheels" will be run by subpostmasters, offering postal and banking services to more isolated areas of the UK.
The Mercedes Sprinter vans, which have an accessibility lift, will cover half-a-million miles over the coming year.
Post Office network director Kevin Gilliland said: "Post Office is modernising to meet customers' needs.
"We are investing in services across our network to make it easier for customers, whether that means they are served via one of our new vehicles in more isolated areas or at a modernised high street branch."
The conversion of the vehicles from standard vans into mobile post office branches is being undertaken by Leicester Carriage Builders, part of the Central England Co-operative Ltd.