First-Class Mail Packages  
Use First-Class Mail for your small packages.
Packages include boxes, thick envelopes, or tubes. If your package is 13 ounces or less, First-Class Mail offers the best value for your postage dollar. If your package weighs more than 13 ounces, you can use Priority Mail.
 
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Find out how much First-Class Mail costs.
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Add Extra Services:

Proof at Deposit

Certificate of Mailing – Provides evidence of mailing.
Certified Mail™ – Provides a mailing receipt and online access to delivery information.
Collect on Delivery – Allows the postage and price of an item to be collected from the recipient by the USPS and given to the mailer.

Protection in Transit
Insured Mail – Insurance against loss or damage for merchandise and gifts.
Registered Mail™ – Provides maximum security and date of delivery or attempted delivery.

Confirmation of Delivery
Delivery Confirmation™ – Provides date and time of delivery or attempted delivery.
Signature Confirmation™ – Provides date and time of delivery or attempted delivery, and requires the signature of the person who accepts the item.

Related Publications
A Customer's Guide to Mailing – A simple, easy-to-understand guide to mailing within the U.S.
First-Class Mail postage prices