Royal Bank of Scotland banking group customers will be able to use Post Office branches to place deposits into their accounts from later this year.
Personal and business customers of RBS as well as its sister banks NatWest and Ulster Bank will be able to pay in cheques or cash in any of the Post Office's 11,500 branches under the plans.
RBS said customers will start using Post Office branches to pay in deposits "later this year" but no exact date has been set.
The group already has a relationship with the Post Office which enables its customers to withdraw cash and check their balances at Post Office branches.
Previous research has found that 99% of people in the UK live within three miles of a Post Office.
The plans were announced amid speculation that RBS may be set to pull out of some riskier investment bank activities and put a renewed focus on retail customers and firms in the coming years.
A report in the Financial Times suggested that this could lead to as many as 30,000 jobs going.
Nick Kennett, director of Post Office Financial Services, said: "We are delighted to extend the services offered to RBS and NatWest personal and business customers through the Post Office."