The UPU Convention divides letter-post items into basic services and three categories of supplementary services (optional, mandatory, and those with both optional and mandatory elements). The limits of weight and size of the various letter-post items are also defined.

Letter volumes have been falling for years owing to digitalization and the changing needs and habits of customers. The COVID-19 pandemic further accelerated the decline. Social mail has decreased more than business mail, partly because some documents need to be physically signed and delivered by law. Domestic letter-post volumes fell by about 4.9% in 2018 and by 13.6% in 2020. International letter-post volumes have continued to decrease by 3% every year. Letter post still makes up the biggest share of postal operators' revenue; however, it fell from an average of 35.4% in 2019 to 32.7% in 2020 – the lowest ever share. In parallel, parcels and logistics make up a growing part of postal operators' income (30%). Postal operators need to find ways to keep the letter-post market alive by introducing new and innovative features, products and services. A number of strategies that DOs could consider to develop the traditional letter-post (documents) market include:

 

• Investing in digitalization;
• Introducing cost-cutting measures and utilizing operational synergies;
• Enhancing quality/speed of service through operational optimization and IT solutions;
• Focusing on certain customer segments and investing in sustainability;
• Diversifying services with a menu of value-added features.