How can one determine if a MySQL server allows connections from external sources?

To determine if a MySQL server allows connections from external sources, you can check the value of the `bind-address` parameter in the MySQL configuration file. If the `bind-address` parameter is set to `0.0.0.0`, it means that the MySQL server is configured to accept connections from any IP address, including external sources. If the `bind-address` parameter is set to `127.0.0.1`, it means that the MySQL server is only accepting connections from the localhost.

// Connect to the MySQL server
$mysqli = new mysqli('localhost', 'username', 'password', 'database');

// Check the bind-address parameter
$result = $mysqli->query("SHOW VARIABLES LIKE 'bind_address'");
$row = $result->fetch_assoc();

if ($row['Value'] == '0.0.0.0') {
    echo 'MySQL server allows connections from external sources';
} else {
    echo 'MySQL server does not allow connections from external sources';
}

// Close the connection
$mysqli->close();