The mail agency will offer a 2 percent postage discount during July and August for letters and cards that use the two-dimensional barcodes, known as QR codes, according to a statement on Monday.

When scanned by Research in Motion's Blackberry, Apple's iPhone and other smartphones, the codes would link to a website selling a product or service or to a mobile-optimized page tailored to the mail recipient.

Groups sometimes use similar codes in television commercials or on posters in public places to promote products or offer information. The Postal Service hopes the codes will allow mailers to more effectively target advertisements.

The Postal Service has been seeking ways to keep advertisers from moving online and to tie digital trends into the mail system. The agency also offers programs to help mailers create and target direct mail, sometimes known as junk mail.

"The integration of direct mail with mobile technologies will not only improve the long-term value of direct mail but also increase returns for merchants," said Gary Reblin, the agency's vice president for domestic products.

Mail volume in the United States has been on the decline since 2006 and fell to 39.5 billion pieces during the most recent quarter, a 4.1 percent drop compared to a year earlier.

The Postal Service lost $3.2 billion in the first three months of 2012. The agency said better-targeted mailings and electronic alternatives eroded advertising mail volumes during the quarter.

Almost 50 percent of U.S. mobile subscribers own a smartphone and one in five of those owners scanned a QR code as of December 2011, the Postal Service said, citing MarketingProfs, a marketing advice group.

Reblin said in the statement that mobile purchases represented 11 percent of e-commerce sales during the 2011 holidays.

(Reporting By Emily Stephenson; Editing by Cynthia Osterman)

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