How can the user ensure that the email is sent successfully without duplication in PHP?

To ensure that the email is sent successfully without duplication in PHP, the user can use a unique identifier, such as a timestamp or a random string, to generate a unique message ID for each email. This message ID can be stored in a database or a file to track sent emails and prevent duplication.

// Generate a unique message ID
$message_id = uniqid();

// Store the message ID in a database or file
// Check if the message ID already exists before sending the email
if (!check_message_id_exists($message_id)) {
    // Send the email
    // Update the database or file with the new message ID
    update_message_id($message_id);
}