The amount of postage needed to mail a 6” x 9” envelope depends on the postal classification rate used for shipping. When mailing to an address within the US, the most popular service is First Class.
Priority Mail Flat Rate, on the other hand, costs more for shipping a few ounces, but it can be less expensive if the envelope is over 3.5 ounces in weight or ¼ inch in thickness.
Priority Mail Express Service offers a flat rate fee that includes several extra services at no additional costs. A 6” x 9” envelope weighing up to 1 ounce requires one $.50 first class rate stamp.
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