SKILL.md
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: "[email protected]", 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