The postal service across the UK has been hit by further disruption as Royal Mail staff began a second day of strike action starting on Thursday evening.
Postal workers staged their first 24-hour strike in June
The Communication Workers Union (CWU) said up to 130,000 of its members walked out at 1900 BST. It follows another stoppage last month.
The union has written to Royal Mail chairman Allan Leighton to outline a deal which could break the deadlock.
It is in dispute with the Royal Mail over the company's 2.5% pay offer.
Union officials have argued that workers' pay should rise in line with inflation, which Royal Mail says it can't afford.
The CWU is also locked in battle with the Royal Mail over its modernisation plans, which they say will lead to the loss of 40,000 jobs.
Royal Mail says that changes are essential in order to compete with rival mail firms.
But the CWU's deputy general secretary, Dave Ward, says that rather than modernising, Royal Mail is "intent on cutting services, cutting jobs and cutting pay".
As the strike was about to began, Royal Mail's Allan Leighton said that "yet again the union has refused to grasp or understand the harsh commercial reality of the market in which Royal Mail now operates".
Since Royal Mail lost its monopoly status on post deliveries from 1 January 2006, 17 operators have entered the UK mail market, creating fierce competition for the post office group - particularly in the more profitable business post sector.
ROYAL MAIL FACTS
The UK mail market is falling by 2.5% per year
Royal Mail has lost 40% of corporate business
Royal Mail rivals will handle one in five of all letters posted in the UK
Royal Mail pays their workers 25% more than rivals
Source: Royal Mail
Royal Mail says they have already lost about 40% of its bulk mail business to rival postal operators.
Most recently, an £8m contract with Amazon and a £12m contract with the Department for Work and Pensions have fallen to private firm UK mail, owner of Business Post.
The company says its needs to spend a £1.2bn loan from the Government to invest in new technology to transform their operations, not in higher wages.
Union representatives met Royal Mail managers on Wednesday in a bid for fresh talks, but a union statement later said the Royal Mail had "simply concentrated on reiterating their previous offer that the workforce has already overwhelmingly rejected".
The Royal Mail said it was "deeply disappointed" that another strike had been called.
A spokesman said: "Further strike action will achieve nothing.
"The union is saying nothing new and is simply ignoring the challenge confronting everyone in Royal Mail which is the absolute need to modernise - as all our major rivals have already done.
"Strike action only makes it even tougher for Royal Mail to secure its future and continue to provide great quality of service for its customers."