SMTP

PHPMailer

Use PHPMailer to send email through the Lettermint SMTP relay from PHP.

This guide covers SMTP integration. For full configuration options and available headers, see the SMTP Introduction.

Installation

Install PHPMailer via Composer:

Code
composer require phpmailer/phpmailer

Basic configuration

Use environment variables for credentials:

Code
<?php
// Load from environment or config
$smtpHost = 'smtp.lettermint.co';
$smtpUsername = 'lettermint';
$smtpPassword = getenv('LETTERMINT_PROJECT_TOKEN'); // Your Project API token

<?php
use PHPMailer\PHPMailer\PHPMailer;
use PHPMailer\PHPMailer\Exception;

require 'vendor/autoload.php';

$mail = new PHPMailer(true);

try {
    // Server settings
    $mail->isSMTP();
    $mail->Host       = 'smtp.lettermint.co';
    $mail->SMTPAuth   = true;
    $mail->Username   = 'lettermint';
    $mail->Password   = getenv('LETTERMINT_PROJECT_TOKEN');
    $mail->SMTPSecure = PHPMailer::ENCRYPTION_STARTTLS;
    $mail->Port       = 587;

    // Recipients
    $mail->setFrom('sender@yourdomain.com', 'Your Name');
    $mail->addAddress('recipient@example.com', 'Recipient Name');

    // Content
    $mail->isHTML(true);
    $mail->Subject = 'Test Email';
    $mail->Body    = '<h1>Hello!</h1><p>This is a test email.</p>';
    $mail->AltBody = 'Hello! This is a test email.';

    $mail->send();
    echo 'Message sent successfully';
} catch (Exception $e) {
    echo "Message could not be sent. Error: {$mail->ErrorInfo}";
}

Advanced features

Multiple recipients

Code
$mail->addAddress('user1@example.com');
$mail->addAddress('user2@example.com');
$mail->addCC('manager@yourdomain.com');
$mail->addBCC('archive@yourdomain.com');

Attachments

Code
$mail->addAttachment('/path/to/file.pdf');
$mail->addAttachment('/path/to/image.jpg', 'custom-name.jpg');

Custom headers

Code
$mail->addCustomHeader('X-Custom-Header', 'Custom Value');
$mail->addCustomHeader('X-Priority', '1');

Lettermint headers

Add Lettermint-specific headers for tags, metadata, and routing:

Code
// Existing singular tag
$mail->addCustomHeader('X-LM-Tag', 'order-confirmation');

// Structured tags. PHPMailer permits repeated custom headers.
$mail->addCustomHeader('X-LM-Tags', 'campaign=orders, environment=production');
$mail->addCustomHeader('X-LM-Tags', 'variant=B');

// Metadata for tracking (included in webhooks)
$mail->addCustomHeader('X-LM-Metadata-order_id', '12345');
$mail->addCustomHeader('X-LM-Metadata-customer_id', 'cust_789');

// Route selection
$mail->addCustomHeader('X-Lettermint-Route', 'transactional');

X-LM-Tag is the singular tag. X-LM-Tags contains structured pairs. Call addCustomHeader again to add another X-LM-Tags field.

See the SMTP Introduction for full details on available headers and their formats.

Nodemailer Python (smtplib)