A php function to check if an email address is truly valid and does exist

IsValidMailbox.php

<?php
function IsValidMailbox($address){
    if(preg_match('/@([^\s]+)/i', $address, $matches)){
        if(dns_get_mx($matches[1], $out)){            
            $timeout = 10; // Timeout for connection
            $mailServer = $out[0];

            // Open a plaintext connection to the mail server. Assuming port 25 outbound isnt blocked here
            $connection = stream_socket_client(
                "$mailServer:25",
                $errno,
                $errstr,
                $timeout,
                STREAM_CLIENT_CONNECT
            );

            if (!$connection) {
                return "Failed to connect: $errstr ($errno)";
            }

            // Step 1: Wait for the 220 response from the server to confirm readiness
            $response = fgets($connection, 512);
            if (substr($response, 0, 3) != '220') {
                fclose($connection);
                return $response;
            }

            // Step 2: Send EHLO command to initiate communication
            $response = sendCommand($connection, "EHLO localhost");
            if (strpos($response, '250') === false) {
                fclose($connection);
                return "EHLO failed.";
            }

            // Step 3: Check if STARTTLS is supported
            if (strpos($response, 'STARTTLS') !== false) {
                // Step 4: Send STARTTLS command
                $response = sendCommand($connection, "STARTTLS");
                if (strpos($response, '220') === false) {
                    fclose($connection);
                    return "STARTTLS failed." . $response;
                }

                // Step 5: Upgrade the connection to secure (TLS)
                stream_socket_enable_crypto($connection, true, STREAM_CRYPTO_METHOD_TLS_CLIENT);

                // Step 6: Reissue EHLO after upgrading to TLS
                $response = sendCommand($connection, "EHLO localhost");
                if (strpos($response, '250') === false) {
                    fclose($connection);
                    return "EHLO after STARTTLS failed.";
                }
            } else {
                fclose($connection);
                return "STARTTLS not supported by the server." . $response;
            }

            $response = sendCommand($connection, "MAIL FROM:<[email protected]>");
            if (strpos($response, '250') === false) {
                fclose($connection);
                return "MAIL FROM Failed.";
            }
            $commands = [
                "RCPT TO:<$address>",           // Email to verify
                "QUIT"
            ];

            $fullResponse = '';
            foreach ($commands as $command) {
                $response = sendCommand($connection, $command);
                $fullResponse .= $response . "\n";
            }

            fclose($connection);

            // Step 8: Check the response for RCPT TO command
            if (strpos($fullResponse, '250') !== false) {
                return "Email exists.";
            } elseif (strpos($fullResponse, '550') !== false) {
                return "Email does not exist.";
            } else {
                return "Unable to verify email.";
            }
        }
    }
    return false;
}

function sendCommand($connection, $command) {
    fwrite($connection, $command . "\r\n");

    $response = '';

    while ($line = fgets($connection, 512)) {
        $response .= $line;

        // If the line doesn't end with a dash, it's the last line of the response
        if (substr($line, 3, 1) != '-') {
            break;
        }
    }

    return $response;
}
var_dump(IsValidMailbox('[email protected]'));

?>