First-class mail is used for postcards, letters, large envelopes, and small packages. First-class mail must weigh 13 ounces or less. Pieces over 13 ounces can be sent as Priority Mail.

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USPS first-class delivery is given priority over standard mail, and local mail will typically be delivered in 2-3 days. Nationally, first-class mail should be delivered in about 4-5 days. First-class mail postage includes forwarding and return services with no additional charge. (ETC)