The Royal Mail has enlisted the help of Paralympic gold medallist Ellie Simmonds in urging people to post early for Christmas.
The last recommended date for sending first-class letters is December 20, but the postal group said it wanted to spread the workload during its busiest time of the year.
Swimmer Simmonds said: "I will be posting my Christmas cards to family and friends early so that they can enjoy them for as long as possible."
Mike Newnham, Royal Mail's chief customer officer, said: "As we do every year, we encourage people to post early and order presents early to help us spread the workload in the run-up to Christmas."
Last posting date for second-class letters is December 18, while for special deliveries it is December 22.
Air mail to Asia, the Far East, Australia and New Zealand should be posted by December 5 to arrive by Christmas.