The Royal Mail dipped slightly below its target for delivering first class letters on time at the end of last year, new figures have shown.
The target for next-day delivery is 93%, but it was 91.2% in the period between September 24 and December 2.
In the same period, the 98.5% target of second class mail delivered within three working days of posting was achieved, while 94.8% of standard parcels were delivered on time, 4.8% ahead of target.
Royal Mail said its performance was affected by the traditional pre-Christmas increase in mail, compounded by bad weather.
Mark Higson, Royal Mail's managing director of operations and modernisation, said: "This is traditionally Royal Mail's toughest quarter with a seasonal increase in mail volumes, notably parcels, and the likelihood of bad weather.
"Our postmen and women work extremely hard to deliver to some of the most demanding quality of service standards in the whole of Europe."
Royal Mail said it continued to deliver the vast majority of mail within its "demanding" quality of service targets in the first three quarters of the 2012/13 financial year.