The postal regulator's report, released in November, showed that among business customers - which represent 80 per cent of the mailing market - only 25 per cent could identify 1 January 2006 as the date the market opens to full competition.
Postcomm chairman Nigel Stapleton noted that, since the market was opened to limited competition more than two years ago, rivals to Royal Mail had won slightly more than 1.5 per cent of the letters market.
"Customers tell us that this is already encouraging Royal Mail to be more responsive to their needs and offer more choice and innovation in postal services," said Stapleton.
"But the development of a fully competitive market is still at an early stage," he added.