Consumers may be willing to accept a reduced number of postal deliveries and the removal of the distinction between first and second class mail, according to new research.
Consumer Focus said people would want a number of "paybacks" for the changes, including longer Royal Mail opening hours and more convenient locations.
Customers would also want greater innovation in the delivery of parcels and packs, said the consumer group.
Its research, taken from 28 focus groups across the UK, found that businesses would only be prepared to lose Saturday deliveries, while residents would accept reduced deliveries during the week.
Robert Hammond, director of postal policy at Consumer Focus, said: "The communications market is changing dramatically and quickly, and post cannot be left behind.
"Consumers tell us that post will still have a role in their lives in five years' time and the postal service must reflect their changing needs. We know that this will require a difficult debate that potentially involves changes to existing regulation and legislation, but that is all the more important that we begin this discussion now.
"There is a growing tension between the substance of the universal postal service and its sustainability. Consumers should not be obliged to pay a premium for a 'gold-plated' service.
"But that means that policymakers will need to think long and hard about how to ensure that technological advance and changing markets deliver good value and service to consumers, particularly the most vulnerable."
Consumers also wanted to maintain the one price goes anywhere pricing structure.
Royal Mail spokesman James Eadie said: "We will study the report in detail. We are committed to the universal service and to keeping the customer at the heart of our business. Anything that provides further insight into what customers want is of value."
Meanwhile, the postal regulator announced details of a cap on the price of second class stamps for large letters and small parcels.
Ofcom said it will be the same cap as for second class ordinary letters, effectively meaning that prices cannot increase by more than 53% over the next seven years.
Stuart McIntosh, Ofcom's group director of competition, said: "Ofcom's decision to extend the safeguard cap to large letters and small parcels will further protect small businesses and vulnerable customers."
Royal Mail spokesman James Eadie said: "Royal Mail don't believe there is a need for this price regulation as the UK packet and parcels market is highly competitive. Nevertheless, we welcome the fact Ofcom has acknowledged the need for Royal Mail to have pricing flexibility and the nature of the cap gives us that."
The current price of a second class stamp for large letters is 69p, compared with 50p for ordinary letters.
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