Skip to main content
The Lettr WordPress plugin replaces the default wp_mail() function with Lettr’s email API. Once activated, every outgoing email from your WordPress site — including emails from WooCommerce, contact form plugins, and any other plugin that uses wp_mail() — is sent through Lettr automatically. No SMTP configuration needed. Just enter your API key and you’re ready to go.

​
Prerequisites

Before you begin, make sure you have:

API Key

Create an API key in the Lettr dashboard

Verified Domain

Add and verify your sending domain
You’ll also need:
  • WordPress 5.8 or higher
  • PHP 7.2 or higher

​
Install the Plugin

1

Download the plugin

Download the latest release as a ZIP from the GitHub repository.
2

Upload and activate

In your WordPress admin panel, go to Plugins → Add Plugin → Upload Plugin, upload the ZIP file, click Install, and activate the plugin.Alternatively, clone or extract the plugin into /wp-content/plugins/lettr and activate it from the Plugins page.
3

Configure your API key

After activation, you’re redirected to the plugin’s setup page. Enter your Lettr API key (starts with lttr_) and configure your sender name and email address.
The sender email must use a domain you’ve verified in the Lettr dashboard. Emails from unverified domains will be rejected.
4

Send a test email

Use the built-in test email feature to confirm everything is working. Check the Lettr logs to verify delivery.

​
How It Works

The plugin overrides WordPress’s built-in wp_mail() function and routes all emails through the Lettr Send Email API. This means:
  • All plugins are covered — WooCommerce order confirmations, Contact Form 7 submissions, password resets, user notifications, and anything else that calls wp_mail().
  • Attachments are supported — File attachments are automatically encoded and sent via the API.
  • HTML and plain text — The plugin detects the content type and sends the appropriate format.
  • Delivery tracking — Every email appears in your Lettr logs with full delivery status, opens, clicks, and bounces.
Since the plugin uses the Lettr HTTP API (not SMTP), there’s no need to open any ports or configure SMTP settings on your server.

​
Troubleshooting

  • Verify your API key is correct and starts with lttr_
  • Ensure the sender email uses a domain verified in Lettr
  • Check the Lettr logs for error details
  • Confirm another plugin hasn’t already overridden wp_mail() — the Lettr plugin shows an admin notice if this conflict is detected
The Lettr plugin replaces the wp_mail() function. If another plugin (e.g. another email delivery plugin) has already declared wp_mail(), the Lettr plugin cannot override it and will display a notice in the admin panel. Deactivate the conflicting plugin to resolve this.
Make sure your sending domain has proper DNS records:
  • SPF — Authorizes Lettr to send on your behalf
  • DKIM — Cryptographically signs your emails
  • DMARC — Tells receivers how to handle unauthenticated mail
See Deliverability Best Practices for more tips.
The plugin reads attachments from the local filesystem. Ensure the file paths passed to wp_mail() are readable by PHP. Temporary files that are deleted before the API request completes will fail silently.

​
Other Integrations

Stripe

Send payment emails from Stripe

Supabase

Auth emails and Edge Functions

​
What’s Next

Sending Domains

Verify your sending domain

Templates

Create reusable email templates

Webhooks

Track delivery events in real-time

Deliverability

Improve email deliverability