Simple PHP example of sending email via SMTP server.

php-smtp-example.php

<?php

// Configure SMTP
$host = 'smtp.yoursmtphost.tld';
$port = 25;
$username = '[email protected]';
$password = 'senderPassword';
$from = '[email protected]';
$name = 'Sender Name';

// Message
$to = '[email protected]';
$subject = 'Your subject comes here';
$message = 'Your message comes here.';

// Send command to stream
function send($fp, $msg)
{
    fwrite($fp, $msg . "\r\n");

    $timeout = microtime(1) + 0.100;
    stream_set_timeout($fp, 0, 0.100);
    $answer = '';
    while (!feof($fp) && microtime(1) <= $timeout) {
        $answer .= fgets($fp, 2048);
    }
    return $answer;
}

// Open stream with SMTP server
$fp = stream_socket_client($host . ':' . $port, $errno, $errstr);

if (!$fp) {

    // Can't create stream...

    echo "$errstr ($errno)<br />\n";

} else {

    // Stream has been successfully created...

    echo 'Connected<br/>';

    // Follow steps required for Envelope...
    // Read more here: https://utcc.utoronto.ca/usg/technotes/smtp-intro.html

    // Say HELO to SMTP server
    $answer = send($fp, 'HELO localhost');
    echo nl2br($answer);

    // Authenticate user with SMTP server
    // Example of Auth with CRAM-MD5
    // All auth types are: PLAIN, LOGIN, NTLM, CRAM-MD5, XOAUTH2

    // Tell to SMTP server that we will authenticate user with CRAM-MD5
    $answer = send($fp, 'AUTH CRAM-MD5');
    echo nl2br($answer);

    // Send back auth credentials to SMTP server
    $challenge = base64_decode(substr($answer, 4));
    $response = base64_encode($username . ' ' . hash_hmac('md5', $challenge, $password));
    $answer = send($fp, $response);
    echo nl2br($answer);

    // Tell to SMTP server the sender email address
    $answer = send($fp, 'MAIL FROM: <' . $from . '>');
    echo nl2br($answer);

    // Tell to SMTP server the recipient email address
    $answer = send($fp, 'RCPT TO: <' . $to . '>');
    echo nl2br($answer);

    // Tell to SMTP server that we will send email message...
    $answer = send($fp, 'DATA');
    echo nl2br($answer);

    // Prepare headers and message
    $name = '=?UTF-8?B?' . base64_encode($name) . '?=';
    $subject = '=?UTF-8?B?' . base64_encode($subject) . '?=';
    $message = base64_encode(iconv(mb_detect_encoding($message, mb_detect_order(), true), 'UTF-8', $message));
    $headers = [];
    $headers[] = 'MIME-Version: 1.0';
    $headers[] = 'Content-Type: text/html; charset=utf-8';
    $headers[] = 'Content-Transfer-Encoding: base64';
    $headers[] = 'From: ' . $name . ' <' . $from . '>';
    $headers[] = 'To: <' . $to . '>';
    $headers[] = 'Subject: ' . $subject;

    // Send headers with message to SMTP server
    $answer = send($fp, implode("\r\n", $headers) . "\r\n" . $message);
    echo nl2br($answer);

    // Message is complete, so tell it to SMTP server
    $answer = send($fp, '.');
    echo nl2br($answer);

    // That's all, tell to SMTP, that we finish communication
    $answer = send($fp, 'QUIT');
    echo nl2br($answer);

    // Close stream
    fclose($fp);
}