The company is urging business customers to avoid a last minute rush by booking collections in advance and accurately forecasting expected volumes.
Christmas is the busiest time of the year for the UK postal operator which begins planning for Christmas as early as April.
The latest recommended posting date for Royal Mail 48 and 2nd Class Royal Mail Business Mail is Tuesday 20 December 2016.
This is followed by Royal Mail Tracked 48, Royal Mail 24 and 1st Class Royal Mail Business Mail on Wednesday 21 December 2016.
For Royal Mail Special Delivery Guaranteed and Royal Mail Tracked 24, customers can post orders up until Thursday 22 December 2016 for guaranteed Christmas delivery.
Royal Mail Special Delivery Saturday Guaranteed items must be in the Royal Mail system by Friday 23 December 2016 if orders are to arrive in time for Christmas Day.
Royal Mail said: “Our business mail services provide a vital link between businesses and their customers all year round and especially during the festive season. As always, we urge customers to talk to us about their expected volumes and to post early to avoid the last minute Christmas rush.”