Royal Mail has seen its half-year operating profit drop 72 per cent from £184m a year earlier.
The loss at Royal Mail Letters totalled £66m, after a £48m profit last year.
Royal Mail said the loss was caused by a continuing fall in mail volumes, and had been limited by cost-cutting.
It said mail volumes fell by a further five per cent during the first half of the year, as more customers used e-mail, websites "and, increasingly, social media for communications in place of the traditional letter".
Royal Mail Letters now delivers 68m items per day on average, 24 pe cent less than in 2005.