Send SMTP emails with PHP

PHP is a great language for sending email with SMTP. PHP provides many functions for sending emails directly or by connecting to an SMTP server. In this post we will discuss the SMTP standard and different ways to send email in PHP using SMTP.

What is the SMTP protocol?

SMTP or simple mail transfer protocol is a standard way to exchange emails between servers and code. If you wish to send email in PHP using SMTP you must first determine the server you wish to connect to. This could be the SMTP server that hosts the recipients email account or your own SMTP server that will send on your behalf.

Most mail providers run an SMTP server on ports 25, 2525, 465 or 578. MailSlurp is a free email provider with an SMTP server available on the following ports:

PHP mail sending methods

As PHP is an old and venerable language there are many ways to send emails. The oldest method is the mail() function. The mail function has been available since PHP4 but it comes with some caveats. Firstly, it requires configuration using the php.ini system files. This can be difficult to set up. Modern PHP applications typically use a higher level library like PHPMailer.

PHPMailer - the most popular PHP mail library

Due to the limitations of the built-in mail function most developers recommend using the open source PHPMailer library. You can install the library using composer composer require phpmailer/phpmailer. Then include the libaries in your php code using vendor autoload to send email using SMTP in PHP.

<?php
require_once(__DIR__ . '/vendor/autoload.php');

use PHPMailer\PHPMailer\SMTP;
use PHPMailer\PHPMailer\PHPMailer;
use PHPMailer\PHPMailer\Exception;

Connect to SMTP servers using PHPMailer

To send SMTP emails in PHP import PHPMailer and configure an instance to use the port and hostname for your SMTP server.

$mail = new PHPMailer(true);
$mail->SMTPDebug = SMTP::DEBUG_SERVER;
$mail->isSMTP();
$mail->SMTPSecure = '';
$mail->SMTPAuth   = true;
$mail->Host       = 'mx.host.com';
$mail->Username   = 'username';
$mail->Password   = 'your password';
$mail->Port       = 2525;

If you use MailSlurp SMTP servers you can use the getImapSmtpAccess method to obtain your username and password:

$smtpAccess = $inboxController->getImapSmtpAccess($inbox1->getId());

Sending SMTP emails using PHP

To actually send an email, first connect to the server and then build the message in parts.

$smtpAccess = $inboxController->getImapSmtpAccess($inbox1->getId());

$mail = new PHPMailer(true);
try {
    // User smtp access to configure PhpMailer for MailSlurp
    $mail->SMTPDebug = SMTP::DEBUG_SERVER;
    $mail->isSMTP();
    $mail->SMTPAuth   = true;
    $mail->Host       = $smtpAccess->getSmtpServerHost();
    $mail->Username   = $smtpAccess->getSmtpUsername();
    $mail->Password   = $smtpAccess->getSmtpPassword();
    $mail->SMTPSecure = '';
    $mail->Port       = $smtpAccess->getSmtpServerPort();

    // test connection (secure disabled)
    $connected = $mail->smtpConnect();
    $this->assertTrue($connected);

    // write email from inbox1 to inbox2
    $mail->setFrom($inbox1->getEmailAddress());
    $mail->addAddress($inbox2->getEmailAddress());
    $mail->isHTML(true);
    $mail->Subject = 'Hello inbox2';
    $mail->Body    = 'This is an <b>HTML</b> message';

    // send the email
    $sent = $mail->send();

    $this->assertTrue($sent);
} catch (Exception $e) {
    echo "Message could not be sent. Mailer Error: {$mail->ErrorInfo}";
    throw new Exception($mail->ErrorInfo);
}

Testing email sending with PhpUnit

When sending emails from your PHP application consider testing email end-to-end using MailSlurp. MailSlurp is a free service for catching emails in disposable accounts. You can connect to servers using SMTP and then verify that emails were received:

<?php
require_once(__DIR__ . '/vendor/autoload.php');

use MailSlurp\ApiException;
use PHPMailer\PHPMailer\SMTP;
use PHPUnit\Framework\TestCase;
use PHPMailer\PHPMailer\PHPMailer;
use PHPMailer\PHPMailer\Exception;

/**
 * Example tests for MailSlurp (using PHP 7.1)
 */
class MailSlurp_SDK_Test extends TestCase
{

    public $config;

    /**
     * Setup mailslurp config for later use
     */
    public function setUp(): void
    {
        // get api key from environment variables (use your own key here)
        $API_KEY = getenv('API_KEY');
        $this->assertNotEmpty($API_KEY, "API Key must not be empty");

        // create configuration with api key
        $this->config = MailSlurp\Configuration::getDefaultConfiguration()->setApiKey('x-api-key', $API_KEY);
    }

    /**
     * @throws ApiException
     * @throws Exception
     */
    public function test_canSendSMTPEmail_usingPhpMailer() {
        // create an inbox
        $inboxController = new MailSlurp\Apis\InboxControllerApi(null, $this->config);
        $inbox1 = $inboxController->createInboxWithOptions(new \MailSlurp\Models\CreateInboxDto([ "inbox_type" => "SMTP_INBOX"]));
        $this->assertStringContainsString("@mailslurp.mx", $inbox1->getEmailAddress());

        $inbox2 = $inboxController->createInbox();
        $smtpAccess = $inboxController->getImapSmtpAccess($inbox1->getId());

        $mail = new PHPMailer(true);
        try {
            // User smtp access to configure PhpMailer for MailSlurp
            $mail->SMTPDebug = SMTP::DEBUG_SERVER;
            $mail->isSMTP();
            $mail->SMTPAuth   = true;
            $mail->Host       = $smtpAccess->getSmtpServerHost();
            $mail->Username   = $smtpAccess->getSmtpUsername();
            $mail->Password   = $smtpAccess->getSmtpPassword();
            $mail->SMTPSecure = '';
            $mail->Port       = $smtpAccess->getSmtpServerPort();

            // test connection (secure disabled)
            $connected = $mail->smtpConnect();
            $this->assertTrue($connected);

            // write email from inbox1 to inbox2
            $mail->setFrom($inbox1->getEmailAddress());
            $mail->addAddress($inbox2->getEmailAddress());
            $mail->isHTML(true);
            $mail->Subject = 'Hello inbox2';
            $mail->Body    = 'This is an <b>HTML</b> message';

            // send the email
            $sent = $mail->send();

            $this->assertTrue($sent);
        } catch (Exception $e) {
            echo "Message could not be sent. Mailer Error: {$mail->ErrorInfo}";
            throw new Exception($mail->ErrorInfo);
        }

        // wait for email to arrive in inbox2
        $waitForController = new MailSlurp\Apis\WaitForControllerApi(null, $this->config);
        $email = $waitForController->waitForLatestEmail($inbox2->getId(), 30000);
        $this->assertStringContainsString("Hello inbox2", $email->getSubject());
        $this->assertStringContainsString("<b>HTML</b>", $email->getBody());
    }
}

Further reading

There are many other ways to send and receive email in PHP using SMTP. See the PHP developer docs for more information.