$message_id = createMessageId("example.com"); echo "Message ID: " . $message_id;In this example, the createMessageId function is called with the argument "example.com" which specifies the domain name of the message ID. The function then generates a unique message ID and assigns it to the $message_id variable. Finally, the message ID is displayed to the user using the echo function. This createMessageId utility function is part of the PHPMailer package library, which is a popular email library for sending and receiving emails using PHP.