What is the correctly formatted Inmarsat-C address book entry for sending communications to a vessel in the AOR-E?

The correct choice for the Inmarsat-C address book entry when sending communications to a vessel in the Atlantic Ocean Region-East (AOR-E) is formatted as "581323500120."

Inmarsat-C addresses follow a specific structure where the first two digits indicate the region of the satellite network. For the AOR-E region, the address must start with "58." This confirms that the vessel is operating under the appropriate satellite coverage needed for AOR-East.

The subsequent numbers in the address represent the specific identifier for the vessel. In this case, "1323500120" completes the address. The total length of the address is essential, as it ensures that communications can be properly routed to the intended recipient vessel without issues.

Adding an extraneous symbol, such as a plus sign, may interfere with the addressing system and the way the communication is processed by the Inmarsat system, thus making it an invalid option. Hence, the choice presented as "581323500120" accurately adheres to the required format, ensuring successful transmission of communications to the vessel in the specified region.