Sending Emails

Sending emails (Mailtrap)

Overview

Mailtrap sends live email over Email API (REST) or SMTP. Two streams apply for API/SMTP: Transactional (non-promotional, app-generated) and Bulk (promotional / marketing volume). Batch is not a third stream: it is how you submit many messages in one request on whichever stream matches the content. Campaigns are a separate product path for promotional mail to Mailtrap contacts. Pair this sheet with the Transactional / Bulk developer pages when building or debugging integrations (including with AI-assisted coding).

How to integrate (preference order)

Preferred order:

1. Plugin or integration for the user's platform (no-code or minimal-config) where available
2. Official SDK for your language when one exists (maintained clients, typed helpers, less room for URL/auth mistakes).
3. HTTP Email API when there is no SDK or the SDK does not fit (direct POST to /api/send or /api/batch with JSON).
4. SMTP only when you really need it (legacy stack, host/platform that only speaks SMTP, or hard constraints that rule out HTTP).

Choosing how to send

Before generating SDK code: read the README of the relevant SDK repository linked in the SDKs section below for current method signatures, constructor options, and examples. Do not rely on memory.

Related skills: authorizing-api-requests (tokens, env vars, auth headers), using-email-templates (template UUID and variables), testing-with-sandbox (safe testing), setting-up-sending-domain (verification before send).

When not to use

• Sandbox only—capturing mail without delivery, reading messages in a sandbox (testing-with-sandbox).
• The main ask is webhooks, step-by-step Campaigns UI setup, or deliverability deep-dives.
• Exhaustive API reference—once the user's path is clear, link the official send docs for full schemas, optional fields, and edge cases.

Quick reference

Email API

SMTP

Tokens

Use $MAILTRAP_API_TOKEN in either Authorization: Bearer ... or Api-Token: .... The same token works on both send.api.mailtrap.io and bulk.api.mailtrap.io as long as its scope covers the stream. Full guidance (scope, storage, rotation) lives in skill authorizing-api-requests.

Rate limits

Use backoff on 429.

JSON body (non-template)

Typical fields include from, to, subject, and text and/or html. Optional: category, custom_variables. Exact request bodies: Transactional send and Bulk send.

Examples (curl)

Transactional send (send.api.mailtrap.io):

curl -X POST https://send.api.mailtrap.io/api/send \
  -H "Authorization: Bearer $MAILTRAP_API_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{
    "from": {"email": "hello@yourdomain.com", "name": "Your App"},
    "to": [{"email": "user@example.com"}],
    "subject": "Hello",
    "text": "Plain text body"
  }'

Bulk stream uses the same path and JSON shape on the bulk host (same env var; the token only needs bulk-stream scope):

curl -X POST https://bulk.api.mailtrap.io/api/send \
  -H "Authorization: Bearer $MAILTRAP_API_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{
    "from": {"email": "hello@yourdomain.com", "name": "Your App"},
    "to": [{"email": "user@example.com"}],
    "subject": "Promotional",
    "html": "<p>HTML body</p>"
  }'

Batch (array of messages; up to 500 per request — see API docs for full schema):

curl -X POST https://send.api.mailtrap.io/api/batch \
  -H "Authorization: Bearer $MAILTRAP_API_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"messages":[{"from":{"email":"a@example.com"},"to":[{"email":"b@example.com"}],"subject":"One","text":"..."}]}'

JSON body (template)

Use template_uuid and template_variables instead of raw text/html to use a template hosted by Mailtrap. Minimal example:

curl -X POST https://send.api.mailtrap.io/api/send \
  -H "Authorization: Bearer $MAILTRAP_API_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{
    "from": {"email": "hello@yourdomain.com", "name": "Your App"},
    "to": [{"email": "user@example.com"}],
    "template_uuid": "your-template-uuid",
    "template_variables": {"user_name": "Jane"}
  }'

See skill using-email-templates and the same API operations as non-template sends.

SDKs

• Node.js
• Python
• PHP
• Ruby
• Java
• .NET
• CLI

Suppressions

Mailtrap automatically manages suppressions for addresses that hard bounce, report spam, or unsubscribe, and will not send emails to these suppressed recipients again. For details, see the Suppressions documentation.

Common mistakes