Residents in West London are among the least likely to see their post delivered on time.
The SW postcode saw 90.5% of first class post delivered within a day in 2015/16, one of the lowest proportions in the UK. The target in 91.5%.
In 2015/16, Royal Mail missed its target of 93% of First Class mail within one day in the area, with 92.5% delivered on time. It also missed the target to deliver 99% of Special Delivery (Next Day) items on time, at 98.5%.
Across the country, 104 out of 118 postcode areas reached the target to deliver 91.5% of first class post on time.
For all of those targets, the Royal Mail did worse than in 2014/15, when it hit the First Class target, delivered 98.7% of Special Delivery post on time, and 109 areas had on time deliveries.
However, it hit targets for Second Class and outgoing European services mail delivered on time, as well as standards for carrying out collections each and the standard for correctly delivered mail.
Royal Mail said the combination of Cyber Week and poor weather in late November had an impact, with the proportion of first class mail delivered on time falling to 91.1% during October to December, and 46 postcodes missing delivery targets.
The Christmas period, from the first Monday in December to the start of the first working day after the New Year public holiday, is exempt from the targets because of exceptionally high mail volumes.
However, Cyber Week, from Friday 27 November to Friday 4 December 2015, fell outside these exemptions while also bringing extra post.
At the same time, Royal Mail said significant disruption in parts of the country due to poor weather and road closures impacted on performance during the period.
Royal Mail believes that if the 2015-16 performance was adjusted to take into account these two factors, an additional 0.31% would be added to the 92.5% reported performance.
It will ask Ofcom to take the impact of Cyber Week and disruption in parts of the country into account for impacted postcode areas and believes if the 2015-16 performance was adjusted for these three factors, an additional 13 post codes would meet or exceed their targets.