basic smtp class in php for sending simple email.

SimpleSMTPMailer.php

<?php
/**
 * SimpleSMTPMailer Class
 * Author: Mario Flores Rey II <mr3y2@yahoo.com>
 *
 * Minimal, pure-PHP SMTP client for sending emails over SMTPS (implicit SSL on port 465).
 * Compatible with PHP 5.6.40+. Used for testing purposes only. Avoid production use.
 *
 * Usage:
 * $mailer = new SimpleSMTPMailer([
 *     'host' => 'smtp.example.com',
 *     'port' => 465,
 *     'username' => 'username@example.com',
 *     'password' => 'your_password_or_app_password',
 *     'from' => 'from@example.com',
 *     'from_name' => 'Sender Name',
 *     'verify_peer' => false,
 *     'timeout' => 30,
 * ]);
 * $mailer->sendMail('recipient@example.com', 'Recipient Name', 'Subject', 'Message body');
 *
 * Limitation Notes:
 * - Implements just enough of the SMTP protocol to authenticate with AUTH LOGIN to send
 *   single simple email message.
 * - For testing, disable certificate verification (not recommended for production).
 * - Only use US ASCII characters. Do not use accented foreign or fancy utf8 characters.
 * - Most providers (Gmail, Office365, etc.) will prefer app passwords or OAuth2 instead.
 */

class SimpleSMTPMailer
{
    const CRLF = "\r\n";

    private $config;
    private $socket;

    /**
     * Constructor
     *
     * @param array $config Configuration array with SMTP settings
     */
    public function __construct(array $config)
    {
        $this->config = (object) array_merge([
            'host' => null,
            'port' => 465,
            'username' => null,
            'password' => null,
            'from' => null,
            'from_name' => null,
            'verify_peer' => false, // For testing only, must override!
            'cafile' => null, // For testing only, must override!
            'timeout' => 30,
            'local_domain' => 'localhost',
        ], $config);
    }

    /**
     * Send an email
     *
     * @param string $to Recipient email address
     * @param string $to_name Recipient name
     * @param string $subject Email subject
     * @param string $body Email body
     * @return bool True on success, false on failure
     */
    public function sendMail($to, $to_name, $subject, $body)
    {
        try {
            $this->connect();
            $this->authenticate();
            $this->sendMessage($to, $to_name, $subject, $body);
            $this->disconnect();

            printf('Message sent successfully.%s', PHP_EOL);
            return true;

        } catch (Exception $error) {
            printf('Error: %s%s', $error->getMessage(), PHP_EOL);
            if ($this->socket) {
                fclose($this->socket);
            }
            return false;
        }
    }

    /**
     * Connect to SMTP server
     *
     * @throws Exception on connection failure
     */
    private function connect()
    {
        if ($this->socket) {
            throw new Exception('Already connected.');
        }

        $context_options = [
            'ssl' => [
                'verify_peer' => (bool) $this->config->verify_peer,
                'verify_peer_name' => (bool) $this->config->verify_peer,
            ],
        ];

        if (!empty($this->config->cafile)) {
            $context_options['ssl']['cafile'] = $this->config->cafile;
        }

        $stream_context = stream_context_create($context_options);
        $remote_address = 'ssl://' . $this->config->host . ':' . $this->config->port;
        $error_number = 0;
        $error_string = '';

        $this->socket = @stream_socket_client(
            $remote_address,
            $error_number,
            $error_string,
            $this->config->timeout,
            STREAM_CLIENT_CONNECT,
            $stream_context
        );

        if (!$this->socket) {
            throw new Exception(sprintf(
                'Failed to connect to %s: (%d) %s',
                $remote_address,
                $error_number,
                $error_string
            ));
        }

        stream_set_timeout($this->socket, $this->config->timeout);

        // Read server banner
        $server_banner = $this->receiveResponse();
        printf('S: %s', $server_banner);

        // Send EHLO
        $response = $this->sendCommand('EHLO ' . $this->config->local_domain);
        printf('S: %s', $response);
    }

    /**
     * Authenticate with SMTP server using AUTH LOGIN
     *
     * @throws Exception on authentication failure
     */
    private function authenticate()
    {
        $response = $this->sendCommand('AUTH LOGIN');
        printf('S: %s', $response);

        if (strpos($response, '334') !== 0) {
            throw new Exception('Server did not accept AUTH LOGIN. Response: ' . $response);
        }

        $response = $this->sendCommand(base64_encode($this->config->username));
        printf('S: %s', $response);

        $response = $this->sendCommand(base64_encode($this->config->password));
        printf('S: %s', $response);

        if (strpos($response, '235') !== 0) {
            throw new Exception('Authentication failed. Response: ' . $response);
        }
    }

    /**
     * Send the actual email message
     *
     * @param string $to Recipient email
     * @param string $to_name Recipient name
     * @param string $subject Email subject
     * @param string $body Email body
     * @throws Exception on send failure
     */
    private function sendMessage($to, $to_name, $subject, $body)
    {
        // MAIL FROM
        $response = $this->sendCommand('MAIL FROM:<' . $this->config->from . '>');
        printf('S: %s', $response);

        if (strpos($response, '250') !== 0) {
            throw new Exception('MAIL FROM command failed. Response: ' . $response);
        }

        // RCPT TO
        $response = $this->sendCommand('RCPT TO:<' . $to . '>');
        printf('S: %s', $response);

        if (strpos($response, '250') !== 0 && strpos($response, '251') !== 0) {
            throw new Exception('RCPT TO command failed. Response: ' . $response);
        }

        // DATA
        $response = $this->sendCommand('DATA');
        printf('S: %s', $response);

        if (strpos($response, '354') !== 0) {
            throw new Exception('Server did not accept DATA command. Response: ' . $response);
        }

        // Build and send email message
        $email_content = $this->buildEmailMessage($to, $to_name, $subject, $body);
        $response = $this->sendSocket($email_content . self::CRLF . '.' . self::CRLF);
        printf('S: %s', $response);

        if (strpos($response, '250') !== 0) {
            throw new Exception('Message was not accepted. Response: ' . $response);
        }
    }

    /**
     * Build the email message with headers and body
     *
     * @param string $to Recipient email
     * @param string $to_name Recipient name
     * @param string $subject Email subject
     * @param string $body Email message content
     * @return string Formatted email message
     */
    private function buildEmailMessage($to, $to_name, $subject, $body)
    {
        $date = date('r'); // RFC 2822 formatted date
        $email_content = implode(self::CRLF, [
            "From: {$this->config->from_name} <{$this->config->from}>",
            "To: {$to_name} <{$to}>",
            "Subject: {$subject}",
            "Date: {$date}",
            'MIME-Version: 1.0',
            'Content-Type: text/plain; charset=UTF-8',
            self::CRLF, // Empty line to separate headers from body
            $body
        ]);

        // Escape lines starting with a dot by prepending another dot
        $email_content = preg_replace('/^\./m', '..', $email_content);

        return $email_content;
    }

    /**
     * Disconnect from SMTP server
     */
    private function disconnect()
    {
        if ($this->socket) {
            $response = $this->sendCommand('QUIT');
            printf('S: %s', $response);
            fclose($this->socket);
            $this->socket = null;
        }
    }

    /**
     * Receive response from SMTP server
     *
     * @return string Server response
     */
    private function receiveResponse()
    {
        $response = '';
        // Read lines until line begins with 3-digit code + space
        while ($line = fgets($this->socket, 515)) {
            $response .= $line;
            // Check if this is the last line of a multi-line response:
            // e.g. "250-something\r\n" continues, "250 something\r\n" ends
            if (preg_match('/^[0-9]{3} /', $line)) {
                break;
            }
        }
        return $response;
    }

    /**
     * Send data to socket and receive response
     *
     * @param string $string Data to send
     * @return string Server response
     */
    private function sendSocket($string)
    {
        fwrite($this->socket, $string);
        return $this->receiveResponse();
    }

    /**
     * Send SMTP command and receive response
     *
     * @param string $command SMTP command
     * @return string Server response
     */
    private function sendCommand($command)
    {
        return $this->sendSocket($command . self::CRLF);
    }
}