WASHINGTON-- Postage rates are going up starting Sunday, but the changes mostly affect businesses. Mailing a recipe to Aunt Mary or a birthday card to Uncle Joe won't cost any extra.

Among the changes, it will cost advertisers more to flood your mailbox with sales offers, and publishers will face higher charges to send you their magazines.

But the basic 44-cent first-class letter rate will stay the same, even though postage overall goes up about 1.7 percent as the price of many other mailings rises.

The post office has been struggling financially as the Internet siphons off a lot of letters, bills and payments that it used to handle. And that has been complicated by the nation's economic slump, which reduced advertising mail.

The agency lost $8.5 billion last year, and the rate increases, which are estimated to bring in an added $340 million this fiscal year, won't make much of a dent in that.

The U.S. Postal Service is limited to increases at or below the rate of inflation, and a request to exceed that was rejected by the independent Postal Regulatory Commission. The post office, which is not subsidized by taxes, is appealing that ruling, but in the meantime is instituting this increase.

Two changes individuals may notice are for post cards and heavier letters.

The unchanged 44-cent rate still covers the first ounce of a letter, but each additional ounce will cost 20 cents, up from 17 cents currently. Thus, that weighty letter that cost 61 cents to mail last year will now cost 64 cents.

To help deal with that change there's a new 20-cent stamp, featuring Gilbert Stuart's famous portrait of George Washington.

For two-ounce wedding invitations, the 2009 stamp featuring a wedding cake will be reissued at 64 cents; and for three-ounce letters there will be a new 84-cent stamp honoring Oveta Culp Hobby, who founded the Women's Army Corps in World War II.

Post cards will go up a penny to 29 cents, and new stamps also will be available for that rate.

With the change in rates, letters to Canada or Mexico increase to 80 cents, up from 75 cents to Canada and 79 cents to Mexico. Letters to other international destinations will remain unchanged at 98 cents.

There will be a variety of price changes for other mailing services, including advertising mail, periodicals and packages, which have complex sets of charges based on size, weight, distance, what percentage of a magazine is advertising and what percentage is editorial matter, and how much of the sorting is done in advance.

The folks who use those rapid priority and express services had an increase in January.