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Test emails

Use Lettermint test addresses to simulate delivery, bounce, and complaint outcomes without sending email to a real recipient.

Why use test addresses?

Test emails sent to @lettermint.dev addresses are:

• Excluded from billing: They do not count toward your monthly email quota
• Excluded from statistics: They do not change your bounce or complaint rates
• Processed instantly: Events are generated within seconds

Test addresses

Send to any of these addresses to trigger specific delivery events:

Address	Simulated Event	Webhook Event
ok@lettermint.dev	Successful delivery	message.delivered
softbounce@lettermint.dev	Soft bounce (mailbox full)	message.soft_bounced
hardbounce@lettermint.dev	Hard bounce (user unknown)	message.hard_bounced
spamcomplaint@lettermint.dev	Delivery + spam complaint	message.delivered → message.spam_complaint
dsn@lettermint.dev	Out-of-band DSN bounce	message.hard_bounced

Sending test emails

Testing with webhooks

Test addresses are most useful when combined with webhooks. Set up a webhook to receive events, then send test emails to verify your handler processes each event type correctly.

Example: verify bounce handling

1. Create a webhook subscribed to message.hard_bounced events
2. Send to hardbounce@lettermint.dev
3. Confirm your webhook receives the event and your application handles it (e.g., marks the address as undeliverable)

Example webhook payload

When you send to softbounce@lettermint.dev, you receive:

Code
{
  "id": "9b0c4a4e-4e29-4d8b-8b3a-3f0f3e6d2f9b",
  "event": "message.soft_bounced",
  "timestamp": "2025-01-31T14:30:00.000Z",
  "data": {
    "message_id": "f47ac10b-58cc-4372-a567-0e02b2c3d479",
    "subject": "Test soft bounce",
    "recipient": "softbounce@lettermint.dev",
    "response": {
      "status_code": 452,
      "enhanced_status_code": "4.2.2",
      "content": "Mailbox full"
    },
    "metadata": {},
    "tag": null,
    "tags": []
  }
}

See Webhook events for the complete payload reference.

Common testing workflows

Integration testing

Use test addresses in your CI/CD pipeline to verify email sending works without sending real emails:

Code
// In your test suite
describe("Email notifications", () => {
  it("handles bounce events gracefully", async () => {
    // Send to test address
    const response = await email
      .from("app@yourdomain.com")
      .to("hardbounce@lettermint.dev")
      .subject("Test")
      .text("Test")
      .send();

    // Verify your webhook handler marks the address as bounced
    // (depends on your application logic)
  });
});

Manual testing

When developing locally, use a tunnel like ngrok to expose your webhook endpoint, then send test emails to verify the full flow.

Troubleshooting

No webhook received

• Check that the webhook is enabled: Disabled webhooks do not send events
• Verify event subscription: Ensure the webhook subscribes to the relevant event type (e.g., message.soft_bounced)
• Allow processing time: Test events typically arrive within 5-10 seconds
• Check webhook logs: View recent deliveries in Dashboard → Route → Webhooks → [Your Webhook]

API returns an error

• Verify Project API token: Ensure your token is valid and can send for the project
• Check "from" address: The sender domain must be verified in your project

Test address not recognized

• Use an exact domain: Use lettermint.dev or the compatible testing.lettermint.co domain (case-insensitive)
• Check for typos: Common mistakes: test.lettermint.co (wrong), lettermint.devm (wrong TLD)

Next steps