You need to add a little more postage to those letters and post cards you send out today. The cost of mailing a first-class letter increased to 37 cents Sunday, with the price of a postcard bumped up to 23 cents. Postal Service spokesperson Carolyn Dotson says they’ve tried to make the transition easy on customers.She says there are three-cent make up stamps available, as well as some new 37-centers. Dotson says if you forget the change, the letter may come back, or arrive with “postage due.” But she says most people keep up with the change.Dotson says some people started putting the extra postage on their letters early. Dotson says the increase is due to several factors such as the anthrax scare and higher fuel prices. Dotson says there are other rate changes that may impact businesses and you can find out about them at your local post office.