As postal workers begin new nationwide stoppages, the government has claimed the current disagreement centres on changes "agreed two years ago".
In 2007, the last national postal strike ended after both sides signed a 14-page agreement on pay and changes to working practices.
BBC employment correspondent Martin Shankleman explores the failures - and successes - of the 2007 deal that was supposed to bring an end to conflict between the Royal Mail and the Communication Workers Union.
The 2007 deal was supposed to prevent future mail disputes
As deals go, the agreement to end the 2007 nationwide postal strike was certainly woolly in parts.
There was plenty of opportunity for both sides to disagree on exactly what it meant in practice.
Take this gem, quoted verbatim: "It's all about managers, reps and employees working sensibly with a bit of give and take, applying equally to all."
At the very least, the tortuous discussions on implementing the agreement have proved that "give and take" has one attribute very much in short supply.
The stated aim of the agreement, which now seems ironic, was to "move away from the adversarial relationships that persist in too many parts of the business".
As members of the Communication Workers Union (CWU) are now out on another nationwide strike, that goal seems further away than ever.
So who is to blame?
We have extracted some of the specific undertakings from the agreement, and asked both sides what happened after the deal was signed.
At the heart of modernising the organisation is the introduction of new technology to speed up the work, and make it more efficient.
Walk sequencing machines were to be trialled using computer programmes to produce the sensible delivery round for a postal worker.
The 2007 deal set a concrete deadline of the end of January 2008 to agree a framework to deal with the trialling and implementation of all new technology and automation.
But two years on, there is still no agreement according to Royal Mail, which says that a framework was twice agreed between negotiators, but each time it was subsequently rejected by the executive committee of the CWU. The union declined to comment.
Another clause in the agreement pledged: "The early shift payment is ceased in delivery on agreement to pay restructuring."
But Royal Mail says that the early shift payment still technically exists, and the company continues to be "keen to discuss pay restructuring with the union".
So in other words it seems nothing has changed.
However, reform in working practises has proved more successful in other areas.
An undertaking from both sides to introduce a normal start time to the working day, of between 0600 and 0630, has been implemented, according to Royal Mail.
And another clause which obliged for all Royal Mail offices to agree a plan for local flexibility has been carried out.
Royal Mail states that "every office drew up a plan that was jointly signed-off by the union and local manager and most have been successfully deployed".
So the 2007 agreement on modernisation has led to some significant changes in the way Royal Mail staff operate.
But with CWU members now out on another nationwide strike, the great prize of replacing confrontation with trust between the two sides, seems as far away as ever.