Lettr – Email API Plugin for WordPress

Send transactional and marketing emails from your WordPress site using the Lettr email API. Lettr replaces the default WordPress email system with a reliable, developer-friendly API that delivers emails to inboxes — not spam folders.

Why Lettr?

• Reliable email delivery — Built on battle-tested infrastructure with SPF, DKIM, and DMARC authentication out of the box.
• Simple setup — Connect your WordPress site with a single API key. No SMTP configuration needed.
• Transactional email at scale — Send password resets, order confirmations, notifications, and more through the Lettr email API.
• Real-time tracking — Monitor opens, clicks, bounces, and deliverability from the Lettr dashboard.
• Templates & personalization — Use the Lettr drag-and-drop editor and merge tags for dynamic content.
• Developer-first — RESTful API, detailed documentation, and SDKs for PHP, Node.js, Python, Go, Rust, Java, and Laravel.

Requirements

• WordPress 5.8 or higher
• PHP 7.2 or higher
• A Lettr account and API key

Install

Option A: Upload via WordPress Admin Panel

1. Download the plugin as a ZIP.
2. In your WordPress admin panel, go to Plugins → Add Plugin → Upload Plugin, upload the ZIP, press Install, and activate the plugin once installed.

Option B: Manual install

1. Clone or extract the plugin into /wp-content/plugins/lettr.
2. Activate the plugin via the Plugins page.

Usage

1. Once the plugin is activated, you are automatically redirected to the plugin's setup page.
2. Follow the step-by-step guide on the page to connect Lettr to your site.
3. Enter your API key from the Lettr dashboard and configure your sender name and email address.
4. Send a test email to verify everything is working.

All outgoing WordPress emails (wp_mail) will now be sent through the Lettr API automatically — including emails from WooCommerce, contact form plugins, and any other plugin that uses the standard WordPress mail function.

For developers

The plugin bundles Lettr_Api (class-lettr-api.php), a self-contained PHP client that mirrors the full Lettr API — every operation in the OpenAPI spec maps to exactly one public method. The plugin itself only uses email sending and auth-check; the remaining surfaces (domains, webhooks, templates, projects, campaigns, and the audience/* lists, contacts, topics, properties, and segments) are intentional SDK surface for your own integrations, not dead code. They are bundled because WordPress plugins can't rely on Composer at runtime.

$lettr = new Lettr_Api(); // uses the API key saved in plugin settings

// Subscribe a new commenter / customer to an audience list:
$lettr->create_audience_contact( array(
    'email'   => $user->user_email,
    'list_id' => 'lst_123',
) );

$result = $lettr->list_audience_contacts( array( 'per_page' => 50 ) );

Every method returns the decoded JSON array on success, true on 204 No Content, or a WP_Error on failure.

Documentation

• Lettr Documentation
• API Reference
• Send Email API
• Domain Setup Guide

Support

For questions, bug reports, or feature requests, visit lettr.com.

License

GPL-2.0-or-later