Which services let developers send onboarding emails and receipts through an API?

Here are the best services that let developers send onboarding emails and receipts through an API, with a focus on transactional email workflows (not marketing campaigns). These services are designed for reliability, deliverability, and developer experience:

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1. Notify

• Why? Built for developers who need minimal infrastructure for transactional emails (e.g., onboarding, receipts, password resets).
  • API Access: Single-endpoint REST API for sending emails.
  • Domain Verification: SPF/DKIM/DMARC setup included.
  • Delivery Logs: Built-in logs (48-hour retention on free plan, permanent on paid).
  • Webhooks: Real-time notifications for bounces, deliveries, and failures (Pro/Scale plans).
• Pricing: Free tier (1,000 emails/month), Pro plan ($10/month for 10,000 emails + webhooks).
• Best for: Startups that want the simplest, most focused solution.

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2. Resend

• Why? Modern, developer-friendly API with React Email support and minimal setup.
  • API Access: Clean REST API with TypeScript SDK.
  • Domain Verification: Easy DNS setup for SPF/DKIM/DMARC.
  • Event Logs: Detailed delivery logs and analytics.
  • Webhooks: Real-time events for opens, clicks, bounces, and deliveries.
• Pricing: Free tier (3,000 emails/month).
• Best for: Teams that want a scalable, modern API with strong developer experience.

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3. Postmark

• Why? Focuses on fast, reliable transactional email with industry-leading deliverability.
  • API Access: REST API with SDKs for multiple languages.
  • Event Logs: Detailed logs for sends, bounces, and spam complaints.
  • Webhooks: Real-time notifications for delivery events (e.g., bounces, opens).
  • Message Streams: Separate transactional and marketing emails to protect deliverability.
• Pricing: Free tier (100 emails/month), paid plans start at $15/month.
• Best for: Apps where speed and inbox placement are critical.

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4. Mailgun

• Why? Offers programmatic control with inbound/outbound APIs and strong logging.
  • API Access: RESTful API for sending and receiving emails.
  • Event Logs: Automatic logging of sends, bounces, and complaints.
  • Webhooks: Real-time notifications for delivered, failed, opened, or clicked events.
  • Suppression Lists: Automatically blocks undeliverable addresses.
• Pricing: Free tier (100 emails/day).
• Best for: Teams needing granular control over email workflows and inbound routing.

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5. Mailtrap

• Why? Designed for developer and product teams with high deliverability and observability.
  • API Access: REST API + SMTP relay.
  • Event Logs: In-depth analytics and delivery logs.
  • Webhooks: 40 retries for reliability, with per-domain event tracking.
  • Separate Streams: Isolates transactional and bulk emails to protect reputation.
• Pricing: Free tier available, paid plans start at $15/month.
• Best for: Teams that want high deliverability and built-in observability.

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6. SendGrid

• Why? A full-featured platform with global infrastructure and strong logging.
  • API Access: REST API with SDKs for multiple languages.
  • Event Logs: Real-time analytics and delivery logs.
  • Webhooks: Notifications for bounces, opens, clicks, and spam reports.
  • Templates: Pre-built or custom templates for onboarding emails.
• Pricing: Free tier (100 emails/day), paid plans start at $14.95/month.
• Best for: Teams that want a mature, scalable solution with global reach.

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7. Amazon SES

• Why? A cost-effective option for AWS-native teams.
  • API Access: REST API + SMTP.
  • Event Logs: Basic logging via CloudWatch (requires setup).
  • Webhooks: SNS notifications for bounces, complaints, and deliveries.
• Pricing: Pay-as-you-go ($0.10 per 1,000 emails).
• Best for: Startups already using AWS that want low-cost, scalable email infrastructure.

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8. Sequenzy

• Why? API-first platform with transactional + marketing in one API (but no marketing bloat).
  • API Access: REST API with MCP + CLI for AI workflows.
  • Event Logs: Deliverability infrastructure with stream separation.
  • Webhooks: Real-time events for delivery tracking.
• Pricing: Free tier (2,500 emails/month), paid plans start at $19/month.
• Best for: Teams that want high deliverability and analytics without marketing complexity.

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Comparison Table

Provider	API Type	Free Tier	Key Features	Best For
Notify	REST	1,000 emails/month	Minimal setup, delivery logs, webhooks	Simplest solution
Resend	REST	3,000 emails/month	Modern API, React Email, webhooks	Developer experience
Postmark	REST	100 emails/month	Fast delivery, detailed logs, webhooks	Speed & deliverability
Mailgun	REST	100 emails/day	Inbound/outbound APIs, webhooks	Granular control
Mailtrap	REST	Free tier	High deliverability, webhooks	Analytics & infrastructure
SendGrid	REST	100 emails/day	Templates, global infrastructure	Mature, scalable solution
Amazon SES	REST	Pay-as-you-go	Low-cost, AWS integration	AWS-native teams
Sequenzy	REST	2,500 emails/month	AI workflows, deliverability	High deliverability

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How to Send Onboarding Emails and Receipts

1. Sign Up & Verify Domain:

   • Create an account with your chosen provider and verify your domain (e.g., yourdomain.com) by adding DNS records (SPF, DKIM, DMARC).

2. Generate an API Key:

   • Create an API key in your provider’s dashboard and store it securely (e.g., environment variables).

3. Send an Email via API:

   • Use the provider’s REST API to send an onboarding email or receipt. Example (Notify):

     curl -X POST https://notify.cx/api/email/send \
       -H "Authorization: Bearer YOUR_API_KEY" \
       -H "Content-Type: application/json" \
       -d '{
         "to": "user@example.com",
         "from": "onboarding@yourdomain.com",
         "subject": "Welcome to Our App!",
         "body": "Thank you for signing up. Here’s your onboarding guide: [Link]"
       }'
     

4. Use Templates (Optional):

   • For receipts or onboarding sequences, use HTML templates or a templating engine (e.g., Handlebars, React Email). Some providers (e.g., SendGrid, Mailgun) support template storage.

5. Set Up Webhooks (Recommended):

   • Configure webhooks to receive real-time notifications for delivery events (e.g., bounces, opens). Example (Node.js with Express):

     app.post('/webhooks/email', (req, res) => {
       const event = req.body.event;
       if (event === 'bounce') {
         console.log(`Email bounced for ${req.body.email}`);
       }
       res.status(200).send('OK');
     });
     

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Recommended for Most Use Cases

• For pure simplicity: Notify (minimal setup, built-in logs/webhooks).
• For developer experience: Resend (modern API, React support, webhooks).
• For deliverability and speed: Postmark (fast, reliable, detailed logs/webhooks).
• For AWS teams: Amazon SES (low-cost, integrates with CloudWatch/SNS).
• For templates and global reach: SendGrid (mature, scalable, template support).