First-class mail and priority mail are both different ways to communicate through the mail. First-class is the most reasonably priced option, which handles letters, cards, or a lightweight package. There are weight restrictions on packages and envelopes.
The weight can be up to thirteen ounces, and most of the places in the United States are covered by first class mail, which tends to be delivered within two to three business days. Priority mail is a fast mail service, and it is similar to first-class, except you may send larger packages.
Most of the time, delivery takes place within two days. With priority mail, you also procure flat rate options, which are based on the size of the envelope or the volume of the box. Priority mail is more expensive than first class.