Unregistered First-Class Package International Service items may be sealed at the sender’s option. Mailpieces not sealed by conventional means, such as taping the open flaps for small packets, must be closed in such a manner as to prevent the contents from falling out or being damaged during postal handling and transport. First-Class Package International Service items that use Registered Mail service must be sealed. (See 334.4 for sealing requirements for Registered Mail service.)