The temporary staff will help sort the Christmas post as well as the increasing amount of online shopping, with a variety of shifts between mid-November and early January.
Around 14,900 people are needed to work in mail centres, distribution sites and data centres across England.
There are also around 1,300 posts in Scotland, 700 in Wales and 500 in Northern Ireland.
Royal Mail Group's express parcels business, Parcelforce Worldwide, is also recruiting around 1,850 extra sorting staff including 830 drivers throughout the UK.
Royal Mail's chief operations officer Sue Whalley said: "Christmas is our busiest time of year. We plan all year round to help ensure we deliver the best possible service for consumers and businesses in the UK at Christmas.
"We make a substantial commitment in additional resources including the recruitment of thousands of temporary workers to handle the festive mailbag and the growing market of online Christmas shopping."
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