Mailpro APIs | Email API, CRM API & SMS API for your applications

Q: How do I get an API key?

Sign in to your Mailpro account and open Settings > API access. You'll find your numeric client ID and your API key (GUID). You can call the APIs directly with those, or exchange them for an OAuth 2.0 / Bearer JWT token from the token endpoint.

Q: Can I send file attachments? What are the limits and cost?

Yes - attach files when you send an email through the Email API (v2) or CRM API (v3): up to 5 files, 10 MB per file and 15 MB total. Send them as Base64-encoded attachments on either API (the Email API also accepts multipart/form-data file uploads). The cost is 1 credit per 500 KB of attachments, with the first 500 KB included in the email's base credit (so attachments up to ~500 KB add nothing extra). Common document and image formats are accepted; executable and script files (.exe, .bat, .js, .vbs, .msi, .jar, .dll and similar) are blocked for security.

Q: Which email address formats are accepted?

Any RFC-compliant address, including sub-addressing with a '+' (for example user+tag@domain.com), which is supported by Gmail, Fastmail, Proton and others.

Three APIs. One platform.

Pick the one you need — or combine all three. JSON-based REST, fully documented, ready to integrate.

Email API

Send transactional and marketing emails, manage address books, track engagement in real time.

→Campaigns & transactional sending
→Address book management
→Open / click / country stats
→Bounce & unsubscribe tracking

View Email API docs →

CRM API

Manage contacts, tags and segments — and send email & SMS to those contacts. Automate workflows across your stack.

→Contact & profile sync
→Tag & segment management
→Workflow automation
→Native Zapier integration

View CRM API docs →

v1.2

SMS API

Send bulk SMS and individual notifications globally, straight from your application.

→Bulk & individual SMS
→International coverage
→Detailed delivery stats
→Message personalization

View SMS API docs →

For developers

Modern tooling, no surprises.

Everything you need to deliver integrations fast and run them with confidence.

REST + JSON

Predictable resources, consistent error shapes, standard HTTP verbs and status codes.

OAuth2 + scoped tokens

Secure authentication, SSL everywhere, rotate keys without downtime.

Interactive Swagger

Try every endpoint live from the docs. Auto-generated, always in sync.

Open-source SDK

Official SDK on GitHub. Issues, examples and contributions welcome.

Webhooks

Real-time events for opens, clicks, bounces and deliveries — push, don't poll.

Predictable rate limits

100 req/min per account. Clear headers, graceful retries, no silent throttling.

Use cases

From signup emails to global SMS — one integration.

Whether you're building a SaaS, an e-commerce platform or an internal tool, our APIs cover the messaging your product needs.

Transactional & marketing email

Welcome flows, password resets, receipts, newsletters and full campaigns — all from the same API.

CRM & contact sync

Keep contact profiles, tags and segments in sync with your product database or any tool via Zapier.

SMS notifications worldwide

Two-factor codes, delivery alerts, appointment reminders — sent globally with detailed reporting.

POST /webhooks · email.opened

200 OK

{
  "event": "email.opened",
  "message_id": "msg_8Hf2k...",
  "recipient": "[email protected]",
  "campaign_id": "cmp_42",
  "country": "CH",
  "user_agent": "Mozilla/5.0",
  "timestamp": "2026-05-20T09:14:22Z"
}

Start building

Everything you need to integrate, in one place.

{ }

Documentation

Explore the complete, interactive documentation for our Email, CRM and SMS APIs. Test endpoints directly via Swagger.

Explore the APIs

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Integration Examples

Ready-to-use code examples to speed up the integration of our APIs into your projects.

View Examples

GitHub SDK

Find our SDK on GitHub to quickly integrate Mailpro APIs into your applications.

GitHub

API — frequently asked questions

Quick answers for developers integrating Mailpro.

How do I get an API key?+

Sign in to your Mailpro account and open Settings → API access. You'll find your numeric client ID and your API key (GUID). You can call the APIs directly with those, or exchange them for an OAuth 2.0 / Bearer JWT token from the token endpoint.

Which authentication methods are supported?+

Three: OAuth 2.0 with PKCE (recommended for third-party apps and platforms like Zapier, Make and n8n), Bearer JWT (legacy), and id_client + API key. A single OAuth token works across the Email, CRM and SMS APIs.

Are the APIs REST or SOAP?+

They are modern REST APIs over HTTPS. Responses are JSON by default (the Email and SMS APIs also support XML), with predictable resources, standard HTTP verbs and status codes.

Is there interactive documentation or a test mode?+

Yes. Every endpoint can be tried live from the interactive Swagger documentation, and you can send test emails and SMS to your own address before going to production.

Which languages and SDKs can I use?+

Any language that speaks HTTP and JSON. We publish an official SDK on GitHub and provide ready-to-use examples in curl, Node.js, Python, PHP and C#.

Do the APIs support webhooks?+

Yes. Subscribe to real-time events — email delivered, opened, clicked, bounced, and SMS delivery reports — delivered as HMAC-SHA256 signed HTTP callbacks.

Can I send transactional emails, not just campaigns?+

Yes. Send a single email to one recipient with custom fields, attachments and optional scheduling, using the Email API or the CRM API.

Can I send file attachments? What are the limits and cost?+

Yes — attach files when you send an email through the Email API (v2) or CRM API (v3): up to 5 files, 10 MB per file and 15 MB total. Send them as Base64-encoded attachments on either API (the Email API also accepts multipart/form-data file uploads). The cost is 1 credit per 500 KB of attachments, with the first 500 KB included in the email's base credit (so attachments up to ~500 KB add nothing extra). Common document and image formats are accepted; executable and script files (.exe, .bat, .js, .vbs, .msi, .jar, .dll, etc.) are blocked for security.

How does SMS pricing work?+

SMS is credit-based. One SMS costs the destination country's credit price multiplied by the number of parts (a long message is split into several parts). Email sending uses email credits.

Which email address formats are accepted?+

Any RFC-compliant address, including sub-addressing with a "+" (for example [email protected]), which is supported by Gmail, Fastmail, Proton and others.

What are the rate limits?+

Requests are rate-limited per account. When you exceed the limit you receive an HTTP 429 response with clear headers, so you can back off and retry gracefully.

Send your first request in minutes.

Create a free Mailpro account, grab your API key and start sending — no credit card required.

Get your API key — free Read the docs

Email, CRM & SMS APIs — built for developers, trusted by teams.