Mailing Standards of the United States Postal Service - International Mail Manual > 2 Conditions for Mailing > 240 First-Class Mail International > 242 Eligibility
Subject to applicable weight and size limits, any article that is otherwise acceptable and not prohibited by the Postal Service or the country of destination may be mailed at the First-Class Mail International price.
The following conditions apply to dutiable merchandise mailed with First–Class Mail International service:
Nondutiable merchandise may be mailed (at the sender’s risk) to countries that do not accept dutiable merchandise. The Postal Service assumes no responsibility for the treatment such items may receive in the country of destination.
Note: Because PS Form 2976 generally denotes dutiable contents, it should be omitted from First-Class Mail International letter-size and flat-size mailpieces weighing less than 16 ounces when the contents are not dutiable (see 123.61).
First-Class Mail International mailpieces are sealed against inspection.
Certificate of mailing service is available for purchase for First-Class Mail International items.
Registered Mail service is available for purchase for First-Class Mail International items, including for such items mailed as Free Matter for the Blind.
For First-Class Mail International items, return receipt service is available for purchase only for items that use Registered Mail service to certain destinations — see the Individual Country Listings for availability and 340 for preparation procedures.