A Post Office that has suffered regular backlogs will start opening on Sundays.
The extra day of opening at Brighton’s delivery office in North Road will start this week.
Royal Mail said the move was intended to make life easier for customers to collect undelivered parcels.
The Brighton delivery office was plagued by repeated backlogs prior to the controversial privatisation of Royal Mail in December.
A spokesman for Royal Mail said the North Road branch had been chosen as one of the delivery offices to take part in the trial because it received among the highest number of parcels in the country.
Operations Director Tony Fox said: “We are continuing to be more customer-responsive and provide more options for people to receive items they have ordered online.
“I am delighted to pilot Sunday afternoon opening at around 100 of our delivery offices across the UK with the highest parcel volumes, including Brighton.”
The Argus regularly receives complaints from angry residents about delays to deliveries.
Long queues reaching around the corner from the branch have become a regular feature – particularly in the run up to Christmas.
Between 2007 and 2012, Royal Mail paid out more than £700,000 in compensation for providing a second-rate service to customers in Sussex.
In March 2012, postmen at the North Road delivery office admitted to The Argus there were 15 skips piled full of undelivered parcels.
Last year, Royal Mail revealed plans to replace delivery routes in and around Lewes, meaning customers would not receive deliveries until as late as 3pm.
When similar changes were made to the routes in Brighton, postal services became chaotic with reports of parcels stacked up in the North Road sorting office for weeks as staff struggled to complete deliveries.
In response, The Argus launched its Sort It Out campaign to put pressure on Royal Mail bosses to tackle delays. Brighton delivery office will open from midday to 4pm from this Sunday.