It's about to cost more to send letters in the mail. On Sunday, the United States Postal Service will increase the cost of a First-Class Forever U.S. Postage Stamp from the current 66 cents to 68 cents. The price of domestic postcard stamps will also rise from 51 cents to 53 cents. And, stamps for international postcards will go up a nickel to one-dollar 55 cents. The postal service says these increases will help provide much-needed revenue. This is the second increase in six months. Grab those Forever stamps before Sunday!