Postal deliveries will be affected by the extra congestion generated by the Olympic Games, with some mail held in the system for an extra day, the Royal Mail said.
A £1 charge will also be introduced by Parcelforce for delivering to parts of London affected by the Games and Paralympics.
Postmen and women will start their delivery rounds earlier because of the extra travelling time they will need due to transport restrictions.
Households and businesses in the capital were urged to post mail earlier in the day than usual, and a day earlier if possible.
Mark Thomson, Olympic director for Royal Mail, said: “Royal Mail is geared up to serve London during the Games. We will continue to collect and deliver six days a week despite the inevitable impact on the capital’s transport system because of the Games.”