Mailtrap Email Integration

Patterns for adding transactional email sending to an application using Mailtrap's Email API and Sandbox, covering authentication, environment separation, and common delivery pitfalls.

When to Activate

• Implementing a "send email" feature (signup confirmation, password reset, notifications, receipts)
• Debugging why emails aren't arriving in dev/staging
• Setting up a project's first email-sending integration
• Reviewing code that calls an email API directly without sandbox separation

Core Concepts

Sandbox vs. Production separation. Mailtrap provides a Sandbox API that captures emails without delivering them, used for dev/staging so test emails never reach real inboxes. Production sending uses a separate, verified-domain endpoint. Never point a dev environment at the production sending endpoint.

Authentication. Requests use a Bearer token in the Authorization header. Tokens are scoped per project; sandbox and production typically use different tokens.

Domain verification. Production sending requires verifying a sending domain via DNS records (SPF, DKIM, DMARC) before Mailtrap will deliver to real recipients. Skipping this causes silent delivery failures or spam-folder placement.

Code Examples

// Sending via Mailtrap's Email API (production)
async function sendEmail(to: string, subject: string, html: string) {
  const response = await fetch("https://send.api.mailtrap.io/api/send", {
    method: "POST",
    headers: {
      "Authorization": `Bearer ${process.env.MAILTRAP_API_TOKEN}`,
      "Content-Type": "application/json",
    },
    body: JSON.stringify({
      from: { email: "no-reply@yourverifieddomain.com", name: "Your App" },
      to: [{ email: to }],
      subject,
      html,
    }),
  });

  if (!response.ok) {
    throw new Error(`Email send failed: ${response.status}`);
  }
  return response.json();
}

// Same call, routed to Sandbox in non-production environments
const MAILTRAP_ENDPOINT = process.env.NODE_ENV === "production"
  ? "https://send.api.mailtrap.io/api/send"
  : `https://sandbox.api.mailtrap.io/api/send/${process.env.MAILTRAP_INBOX_ID}`;

Anti-Patterns

Anti-Pattern	Why It's a Problem	Instead
Using the production sending endpoint in dev/test	Real test emails reach real inboxes, risking spam complaints and leaked test data	Route non-production environments to the Sandbox endpoint
Hardcoding API tokens in source	Credential leak risk if committed to version control	Load tokens from environment variables / secrets manager
Sending before domain verification completes	Emails silently fail or land in spam	Verify SPF/DKIM/DMARC records before enabling production sending
No retry/error handling on send failures	Silent notification failures (e.g., user never gets password reset email)	Check response status, log failures, surface actionable errors

Best Practices

• Keep sandbox and production tokens in separate environment variables, never share one token across environments
• Verify sending domain DNS records before any production launch involving email
• Log delivery failures with enough context to debug (recipient, template, timestamp, response code)
• Treat email sending as a fallible network call: wrap in try/catch, never assume success

Related Skills

api-and-interface-design, security-and-hardening, ci-cd-and-automation