Some things MUST be mailed as First-Class Mail (or Minimum Quantity to Mail at Commercial Prices:įirst-Class Mail letter-size pieces that are square, rigid or meet at least one of the nonmachinable characteristics are subject to the nonmachinable surcharge.įlat-size pieces that are rigid, nonrectangular, or have uneven thickness will pay the parcel price.Īll mailable matter can be mailed as First-Class Mail. Maximum Weight: 13 ounces (over 13 ounces, First-Class Mail becomes

USPS Marketing Mail Eligibility Decision Tree.Designing Letter and Reply Mail (PUB 25).