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What is the busiest mailing day of the year?

December 15 marked the busiest mailing day of the year as people dispatch holiday cards and presents to friends and relatives across the country.

More than 640 million cards, letters and packages are expected to be processed Monday, the Postal Service announced. Last year the busiest mailing day saw the agency handle 607 million pieces of mail. They attributed the growth to an increase in advertising and mail package volume, as nearly 3.5 million more Americans are expected to shop online this year, a double-digit percentage increase over previous years.

"We are ready for the rush and ready to deliver," said Postmaster General Patrick Donahoe. "This isn't just our busiest time of year -- it's our season. Customers can count on the Postal Service to deliver their holiday gifts in time for Christmas as we have for the past 239 years."

The Postal Service began delivering packages seven days a week in major cities and other high volume areas on Nov. 17, and will continue to do so through Christmas Day in order to keep up with demand. Dec. 20 is the deadline to send greeting cards, packages and letters to ensure they will be delivered in time for Christmas.

For those willing to spring for Priority Mail Express, Dec. 23 is the deadline.

The Postal Service is not funded by taxpayer dollars and instead relies on the sale of postage, products and services to pay for its operating expenses. But the agency still lost $2 billion in the spring even though it has increased its volume and charges consumers more to send mail.

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