Posties are set to walk out on strike at least 19 more times over a pay deal which fails to recognise the cost-of-living crisis.
Union leaders have asked the public to "stand with their local postal worker" as they continue the "fight of their lives".
The Communication Workers Union (CWU), which represents Royal Mail workers, said strikes featuring all workers will take place on 13, 20, and 25 October, and 28 November.
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Different departments and personnel at Royal Mail will strike on other dates, yet to be confirmed, which will affect deliveries on those dates.
Following negotiations between the union and Royal Mail earlier this year workers were offered a two per cent increase by bosses, with a further 1.5 per cent dependent on the erosion of terms and conditions and a £500 “above and beyond” bonus for reaching targets, which union reps say even the company knows are unachievable.
With union members refusing to accept the ripping up of their terms and conditions, they say the offer amounts to 2 per cent and nothing more.
And with economic experts predicting that inflation will rise as high as 18 per cent next year, two per cent represents a real-terms pay cut of 16 per cent. Meanwhile, the company reported record profits of £758 million in 2022.
Speaking of the new strike date, CWU General Secretary Dave Ward said: “This is a significant announcement, but it is one which matches the level of anger our members feel at the way Royal Mail Group has treated them.
“The CEO of Royal Mail Group, Simon Thompson, is treating postal workers as if they are stupid.
“These are the same people that have kept the country connected and returned Royal Mail Group to record profit.
“Postal workers across the UK now face the fight of their lives to save their jobs and the service they provide to every household and business in the UK.
“We call on everyone to stand with their local postal worker.
“If Royal Mail Group are allowed to get away with this then it sends a green light to every rogue big business in the UK.
“We will not stand by and see the Royal Mail Group become the next P&O but we need your backing to win.”
A Royal Mail spokesperson said the firm is losing £1 million a day. This is based on the figures of the previous year, when coronavirus lockdowns were still in place and many people were spending more time at home. They say they've lost £92 million in the first quarter of 2022. If that trend continued they would still stand to make £390 million profit.
A spokesperson said: "Royal Mail needs to adapt much faster to adapt to changing customer demands in a highly competitive market. The CWU has blocked any meaningful discussion on the change agenda the company has set out, and has not put forward any viable alternatives that will fund further pay increases..
They also say that they are planning an attack on the union's bargaining powers, saying union organising is "frustrating transformation".
They said: "Royal Mail has informed CWU that it wants to modernise the ways of working with them. As part of this, Royal Mail will review or serve notice on a number of historic agreements and policies which are currently being used by the CWU to frustrate transformation, and intends to move to a more modern industrial relations framework designed to make the business more agile, and able to compete more effectively."
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