(Reuters) - The U.S. Postal Service's losses shot up to $3.3 billion in the last three months of 2011, a tenfold jump from the same period a year before, as its customer base eroded with the growth of email and online billing.

The cash-strapped agency recorded the loss during its traditionally strongest period, the year-end holiday shipping season, as declines in mail volumes outweighed growth in shipping.

"Technology continues to have a major impact on how our customers use the mail," Postmaster General Patrick Donahoe said in a statement on Thursday.