Royal Mail staff raised £2.6m through payroll giving in the last financial year – up almost £440,000 on the previous 12 months.
About 50,000 Royal Mail employees now make monthly payroll contributions – at a rate of £295 an hour.
An extra 7,000 new participants have been recruited to the scheme over the past year alone; between them donating to more than 850 charities.
Royal Mail was among the first organisations to set up payroll giving in 1989, and its scheme is one of the largest in the UK. The organisation has set itself the target of raising £5m a year through payroll by 2013.
Kay Allen, head of social policy at Royal Mail Group, said: "Each and every one of our 'payroll posties' should be congratulated on their efforts – they are part and parcel of an incredible success story.
"With their support, we've already reached the half-way milestone for the £5m target, and will continue to work hard to generate even further revenue for the hundreds of charities that already benefit from the scheme."
According to the Institute of Fundraising, almost 620,000 employees across the UK donated £62.4m through payroll between April and December 2006.