The First-Class Mail International classification encompasses all categories of international mail that prior to May 14, 2007, were categorized as airmail letter-post and economy letter-post, postcards, printed matter, and small packets that were formerly categorized as LC (letters and cards) and AO (other articles).
Any article that is otherwise acceptable and not prohibited by the Postal Service or country of destination, subject to applicable weight and size limits, may be mailed at the First-Class Mail International price.
Light-colored envelopes and cards that do not interfere with the reading of the address and postmark must be used. Do not use brilliant colors.
Envelopes, cards, and packaging materials must be constructed strong enough to withstand normal handling. Highly glazed paper or paper with a design that affects readability or processing is not acceptable.
Window envelopes must be used under the following conditions:
- For letter-size envelopes only, the address window must be parallel with the length of the envelope.
- For letter-size envelopes only, the address window must be in the lower portion of the address side.
- Nothing but the name, address, and any key number used by the mailer may appear through the address window.
- The return address should appear in the upper-left corner. If there is no return address and the delivery address does not show through the window, the piece will be handled as undeliverable mail.
- The address disclosed through the window must be on white paper or paper of a very light color.
- When used for Registered Mail, window envelopes must conform to the conditions in DMM 503.
- Open panel envelopes — i.e., those in which the panel is not covered with a transparent material — are not acceptable in international mail.
Envelopes and cards that have green-colored bars or red- and blue-striped borders may be used for the sending of First-Class Mail International items.