The Post Office suffered disruption this week after thousands of branches were hit by a computer crash.
The problems hit for two 30-minute periods on Monday afternoon, which left some branches unable to handle the usual volume of mail.
There was a problem with the Horizon system used by Post Offices around the country. The service has now been restored.
“We are very sorry for the inconvenience this problem has caused customers. We know how important the Post Office is to our customers at all times, but especially at Christmas,” said Kevin Gilliland, network and sales director at the Post Office.
According to reports, staff had to manually calculate the cost of sending goods and then stick on individual stamps on one of the busiest days of the year for the Post Office with Christmas approaching.
About 4,000 branches were affected.
Previous Post Office system problems
The Post Office also suffered a glitch back in July, which meant customers were unable to complete card transactions across all branches.
Debit and credit card transactions using Chip and PIN pads at branch counters and Post Office Card Accounts were affected, with customers unable to complete transactions or access their accounts.
The Horizon system is currently at the centre of a potential legal action against the Post Office. Over 80 sub-postmasters are interested in taking legal action against the Post Office in relation to Horizon, which has allegedly has led to false accounting accusations against them.