USPS depends it on the way you ship the mail.
Priority Mail Express (Overnight Delivery Guarantee)
This is the fastest domestic service, with limited exceptions, available 365 days a year, with a money-back guarantee1 and delivery shipping to most U.S. addresses, including PO Boxes. No weighing or calculating needed up to 70 lbs. Flat Rate envelopes affordable pricing offers one rate to any state. Starting at $23.75 at Post Office locations and online.
Priority Mail (1-3 Business Days)
No weighing or calculating needed up to 70 lbs. Flat Rate offers one rate to any state. Beginning at $6.65 at Post Office™ locations and online.
First-Class Mail (1-3 Business Days)
This is a fast, affordable way to send envelopes and lightweight packages. It’s perfect for business and personal correspondence, cards, brochures, and lightweight merchandise (for mail up to 13 oz). The First-Class Mail Forever® Stamp price is $0.49; First-Class Mail Postcard Stamp price is $0.34.
Check out these examples showing how mailing services can be combined to meet your needs shared by USPS.com.