smtp2go-api

SMTP2GO API Integration

Build email and SMS delivery with the SMTP2GO transactional API.

Quick Start

// Send email with SMTP2GO
const response = await fetch('https://api.smtp2go.com/v3/email/send', {
  method: 'POST',
  headers: {
    'Content-Type': 'application/json',
    'X-Smtp2go-Api-Key': env.SMTP2GO_API_KEY,
  },
  body: JSON.stringify({
    sender: '[email protected]',
    to: ['[email protected]'],
    subject: 'Hello from SMTP2GO',
    html_body: '<h1>Welcome!</h1><p>Your account is ready.</p>',
    text_body: 'Welcome! Your account is ready.',
  }),
});

const result = await response.json();
// { request_id: "uuid", data: { succeeded: 1, failed: 0, email_id: "1er8bV-6Tw0Mi-7h" } }

Base URLs

Region	Base URL
Global	https://api.smtp2go.com/v3
US	https://us-api.smtp2go.com/v3
EU	https://eu-api.smtp2go.com/v3
AU	https://au-api.smtp2go.com/v3

Authentication

Two methods supported:

// Method 1: Header (recommended)
headers: {
  'X-Smtp2go-Api-Key': 'your-api-key'
}

// Method 2: Request body
body: JSON.stringify({
  api_key: 'your-api-key',
  // ... other params
})

Get API keys from SMTP2GO dashboard: Sending > API Keys

Core Endpoints

Send Standard Email

POST /email/send

interface EmailSendRequest {
  // Required
  sender: string;           // Verified sender email
  to: string[];             // Recipients (max 100)
  subject: string;

  // Content (at least one required)
  html_body?: string;
  text_body?: string;

  // Optional
  cc?: string[];            // CC recipients (max 100)
  bcc?: string[];           // BCC recipients (max 100)
  reply_to?: string;
  custom_headers?: Array<{ header: string; value: string }>;
  attachments?: Attachment[];
  inlines?: InlineImage[];

  // Templates
  template_id?: string;
  template_data?: Record<string, any>;

  // Subaccounts
  subaccount_id?: string;
}

interface Attachment {
  filename: string;
  mimetype: string;
  fileblob?: string;        // Base64-encoded content
  url?: string;             // OR URL to fetch from
}

interface InlineImage {
  filename: string;
  mimetype: string;
  fileblob: string;
  cid: string;              // Content-ID for HTML reference
}

Response:

interface EmailSendResponse {
  request_id: string;
  data: {
    succeeded: number;
    failed: number;
    failures: string[];
    email_id: string;
  };
}

Send MIME Email

POST /email/mime

For pre-encoded MIME messages:

const response = await fetch('https://api.smtp2go.com/v3/email/mime', {
  method: 'POST',
  headers: {
    'Content-Type': 'application/json',
    'X-Smtp2go-Api-Key': env.SMTP2GO_API_KEY,
  },
  body: JSON.stringify({
    mime_email: mimeEncodedString,
  }),
});

Attachments

Base64 Encoding

// Convert file to base64
const fileBuffer = await file.arrayBuffer();
const base64 = btoa(String.fromCharCode(...new Uint8Array(fileBuffer)));

const email = {
  sender: '[email protected]',
  to: ['[email protected]'],
  subject: 'Document attached',
  text_body: 'Please find the document attached.',
  attachments: [{
    filename: 'report.pdf',
    fileblob: base64,
    mimetype: 'application/pdf',
  }],
};

URL Reference (Cached 24h)

const email = {
  sender: '[email protected]',
  to: ['[email protected]'],
  subject: 'Image attached',
  text_body: 'Photo from our event.',
  attachments: [{
    filename: 'photo.jpg',
    url: 'https://cdn.example.com/photos/event.jpg',
    mimetype: 'image/jpeg',
  }],
};

Inline Images in HTML

const email = {
  sender: '[email protected]',
  to: ['[email protected]'],
  subject: 'Newsletter',
  html_body: '<h1>Welcome</h1><img src="cid:logo123" alt="Logo">',
  inlines: [{
    filename: 'logo.png',
    fileblob: logoBase64,
    mimetype: 'image/png',
    cid: 'logo123',  // Reference in HTML as src="cid:logo123"
  }],
};

Limits: Maximum total email size: 50 MB (content + attachments + headers)

Templates

Create Template

POST /template/add

const response = await fetch('https://api.smtp2go.com/v3/template/add', {
  method: 'POST',
  headers: {
    'Content-Type': 'application/json',
    'X-Smtp2go-Api-Key': env.SMTP2GO_API_KEY,
  },
  body: JSON.stringify({
    template_name: 'welcome-email',
    html_body: '<h1>Welcome, {{ name }}!</h1><p>Thanks for joining {{ company }}.</p>',
    text_body: 'Welcome, {{ name }}! Thanks for joining {{ company }}.',
  }),
});

Send with Template

const email = {
  sender: '[email protected]',
  to: ['[email protected]'],
  subject: 'Welcome aboard!',
  template_id: 'template-uuid-here',
  template_data: {
    name: 'John',
    company: 'Acme Corp',
  },
};

Template Syntax: HandlebarsJS with {{ variable }} placeholders.

Template Endpoints

Endpoint	Method	Description
/template/add	POST	Create new template
/template/edit	POST	Update existing template
/template/delete	POST	Remove template
/template/search	POST	List/search templates
/template/view	POST	Get template details

Webhooks

Configure webhooks to receive real-time delivery notifications.

Event Types

Email Events:

Event	Description
processed	Email queued for delivery
delivered	Successfully delivered
open	Recipient opened email
click	Link clicked
bounce	Delivery failed
spam	Marked as spam
unsubscribe	User unsubscribed
resubscribe	User resubscribed
reject	Blocked (suppression/sandbox)

SMS Events:

Event	Description
sending	Processing
submitted	Sent to provider
delivered	Confirmed delivery
failed	Delivery failed
rejected	Network blocked
opt-out	Recipient opted out

Webhook Payload (Email)

interface WebhookPayload {
  event: string;
  time: string;           // Event timestamp
  sendtime: string;       // Original send time
  sender: string;
  from_address: string;
  rcpt: string;           // Recipient
  recipients: string[];
  email_id: string;
  subject: string;
  bounce?: string;        // Bounce type if applicable
  client?: string;        // Email client (for opens)
  'geoip-country'?: string;
}

Webhook Configuration

POST /webhook/add

await fetch('https://api.smtp2go.com/v3/webhook/add', {
  method: 'POST',
  headers: {
    'Content-Type': 'application/json',
    'X-Smtp2go-Api-Key': env.SMTP2GO_API_KEY,
  },
  body: JSON.stringify({
    url: 'https://api.yourdomain.com/webhooks/smtp2go',
    events: ['delivered', 'bounce', 'spam', 'unsubscribe'],
  }),
});

Webhook Endpoints

Endpoint	Method	Description
/webhook/view	POST	List webhooks
/webhook/add	POST	Create webhook
/webhook/edit	POST	Update webhook
/webhook/remove	POST	Delete webhook

Retry Policy: Up to 35 retries over 48 hours. Timeout: 10 seconds.

Statistics

Email Summary

POST /stats/email_summary

Combined report of bounces, cycles, spam, and unsubscribes.

const response = await fetch('https://api.smtp2go.com/v3/stats/email_summary', {
  method: 'POST',
  headers: {
    'Content-Type': 'application/json',
    'X-Smtp2go-Api-Key': env.SMTP2GO_API_KEY,
  },
  body: JSON.stringify({}),
});

Statistics Endpoints

Endpoint	Method	Description
/stats/email_summary	POST	Combined statistics
/stats/email_bounces	POST	Bounce summary (30 days)
/stats/email_cycle	POST	Email cycle data
/stats/email_history	POST	Historical data
/stats/email_spam	POST	Spam reports
/stats/email_unsubs	POST	Unsubscribe data

Activity Search

POST /activity/search (Rate limited: 60/min)

Search for email events:

const response = await fetch('https://api.smtp2go.com/v3/activity/search', {
  method: 'POST',
  headers: {
    'Content-Type': 'application/json',
    'X-Smtp2go-Api-Key': env.SMTP2GO_API_KEY,
  },
  body: JSON.stringify({
    // Filter parameters
  }),
});

Note: Returns max 1,000 items. For real-time data, use webhooks instead.

Suppressions

Manage email addresses that should not receive emails.

Add Suppression

POST /suppression/add

await fetch('https://api.smtp2go.com/v3/suppression/add', {
  method: 'POST',
  headers: {
    'Content-Type': 'application/json',
    'X-Smtp2go-Api-Key': env.SMTP2GO_API_KEY,
  },
  body: JSON.stringify({
    email: '[email protected]',
  }),
});

Suppression Endpoints

Endpoint	Method	Description
/suppression/add	POST	Add to suppression list
/suppression/view	POST	View suppressions
/suppression/remove	POST	Remove from list

SMS

POST /sms/send

const response = await fetch('https://api.smtp2go.com/v3/sms/send', {
  method: 'POST',
  headers: {
    'Content-Type': 'application/json',
    'X-Smtp2go-Api-Key': env.SMTP2GO_API_KEY,
  },
  body: JSON.stringify({
    to: ['+61400000000'],  // Max 100 numbers
    message: 'Your verification code is 123456',
  }),
});

SMS Endpoints

Endpoint	Method	Description
/sms/send	POST	Send SMS
/sms/received	POST	View received SMS
/sms/sent	POST	View sent SMS
/sms/summary	POST	SMS statistics

Response Codes

Code	Status	Description
200	OK	Success
400	Bad Request	Invalid parameters
401	Unauthorized	Invalid/missing API key
402	Request Failed	Valid params, request failed
403	Forbidden	Insufficient permissions
404	Not Found	Resource not found
429	Too Many Requests	Rate limited
5xx	Server Error	SMTP2GO server issue

Error Response Format

interface ErrorResponse {
  request_id: string;
  data: {
    error: string;
    error_code: string;
    field_validation_errors?: Record<string, string>;
  };
}

Common error codes:

• E_ApiResponseCodes.ENDPOINT_PERMISSION_DENIED - API key lacks permission
• E_ApiResponseCodes.NON_VALIDATING_IN_PAYLOAD - Invalid JSON/email format
• E_ApiResponseCodes.API_EXCEPTION - General API error

Rate Limiting

• Activity Search: 60 requests/minute
• Email Search (deprecated): 20 requests/minute
• Other endpoints: Configurable per API key

Handling 429:

async function sendWithRetry(payload: any, maxRetries = 3) {
  for (let i = 0; i < maxRetries; i++) {
    const response = await fetch('https://api.smtp2go.com/v3/email/send', {
      method: 'POST',
      headers: {
        'Content-Type': 'application/json',
        'X-Smtp2go-Api-Key': env.SMTP2GO_API_KEY,
      },
      body: JSON.stringify(payload),
    });

    if (response.status === 429) {
      await new Promise(r => setTimeout(r, Math.pow(2, i) * 1000));
      continue;
    }

    return response.json();
  }
  throw new Error('Rate limit exceeded after retries');
}

Cloudflare Workers Integration

// wrangler.jsonc
{
  "name": "email-service",
  "vars": {
    "SMTP2GO_REGION": "api"  // or "us-api", "eu-api", "au-api"
  }
}

// .dev.vars
SMTP2GO_API_KEY=api-XXXXXXXXXXXX

// src/index.ts
export default {
  async fetch(request: Request, env: Env) {
    const baseUrl = `https://${env.SMTP2GO_REGION}.smtp2go.com/v3`;

    // Send transactional email
    const response = await fetch(`${baseUrl}/email/send`, {
      method: 'POST',
      headers: {
        'Content-Type': 'application/json',
        'X-Smtp2go-Api-Key': env.SMTP2GO_API_KEY,
      },
      body: JSON.stringify({
        sender: '[email protected]',
        to: ['[email protected]'],
        subject: 'Order Confirmation',
        template_id: 'order-confirmation-template',
        template_data: {
          order_id: '12345',
          total: '$99.00',
        },
      }),
    });

    const result = await response.json();
    return Response.json(result);
  },
} satisfies ExportedHandler<Env>;

interface Env {
  SMTP2GO_API_KEY: string;
  SMTP2GO_REGION: string;
}

Sender Verification

Before sending, verify your sender identity:

1. Sender Domain (Recommended): Add and verify domain in SMTP2GO dashboard for SPF/DKIM alignment
2. Single Sender Email: Verify individual email address

Unverified senders are rejected with 400 error.

Common Patterns

Contact Form Handler

export async function handleContactForm(formData: FormData, env: Env) {
  const name = formData.get('name') as string;
  const email = formData.get('email') as string;
  const message = formData.get('message') as string;

  const response = await fetch('https://api.smtp2go.com/v3/email/send', {
    method: 'POST',
    headers: {
      'Content-Type': 'application/json',
      'X-Smtp2go-Api-Key': env.SMTP2GO_API_KEY,
    },
    body: JSON.stringify({
      sender: '[email protected]',
      to: ['[email protected]'],
      reply_to: email,
      subject: `Contact form: ${name}`,
      text_body: `From: ${name} <${email}>\n\n${message}`,
      html_body: `
        <p><strong>From:</strong> ${name} &lt;${email}&gt;</p>
        <hr>
        <p>${message.replace(/\n/g, '<br>')}</p>
      `,
    }),
  });

  if (!response.ok) {
    throw new Error('Failed to send email');
  }

  return response.json();
}

Webhook Handler

export async function handleWebhook(request: Request) {
  const payload = await request.json();

  switch (payload.event) {
    case 'bounce':
      // Handle bounce - update user record, retry logic
      console.log(`Bounce: ${payload.rcpt} - ${payload.bounce}`);
      break;

    case 'unsubscribe':
      // Update preferences
      console.log(`Unsubscribe: ${payload.rcpt}`);
      break;

    case 'spam':
      // Add to suppression, alert team
      console.log(`Spam report: ${payload.rcpt}`);
      break;
  }

  return new Response('OK', { status: 200 });
}

Troubleshooting

Issue	Cause	Solution
401 Unauthorized	Missing/invalid API key	Check API key in header or body
400 sender not verified	Unverified sender domain	Verify domain in SMTP2GO dashboard
429 Too Many Requests	Rate limit exceeded	Implement exponential backoff
Attachment too large	Over 50MB total	Compress or use URL references
Template variables not replaced	Wrong syntax	Use {{ variable }} Handlebars syntax
Webhook not receiving events	Timeout/errors	Check endpoint returns 200 within 10s

References

• SMTP2GO API Documentation
• API Reference
• Getting Started Guide
• Webhook Documentation
• Template Guide

---

Last Updated: 2026-02-06 API Version: v3.0.3