Transactional emails are critical to modern digital platforms. Whether you’re confirming a purchase, resetting a password, or sending an invoice, these emails need to arrive instantly, reliably, and securely.

While many businesses turn to premium email service providers, not every startup or developer has the budget for it. That’s where free transactional email API services step in—offering robust, scalable, and feature-rich solutions at no cost (at least up to a certain limit).

In this guide, we’ll explore the best free transactional email APIs, key features to look for, and how to get started. Let’s dive into the top players in 2025!

What Is a Transactional Email API?

A transactional email API allows developers to programmatically send automated, real-time emails. These messages are triggered by user actions—such as creating an account, completing a purchase, or updating a password.

Unlike bulk marketing emails, transactional emails are personalized, event-driven, and essential for maintaining user trust.

Common Use Cases:

Welcome emails
Order confirmations
Shipping updates
Password resets
Account notifications
Invoice and billing alerts

Top Free Transactional Email API Services (2025)

Let’s explore the best free services offering transactional email APIs with generous plans, solid uptime, and developer-friendly tools.

1. Sendinblue (Brevo)

Free Plan:

300 emails/day
Unlimited contacts
API access
SMTP relay

Why it’s great:
Brevo (formerly Sendinblue) offers a clean interface, excellent deliverability, and advanced email tracking.

Key Features:

Real-time analytics
Custom SMTP
Email templates
Drag-and-drop editor
Marketing automation (with upgrades)

Best For:
Startups and small businesses who want both transactional and marketing capabilities.

2. Mailgun

Free Plan:

5,000 emails/month for 30 days
Powerful RESTful API
Email tracking and logs
SMTP integration

Why it’s great:
Mailgun is built for developers. It offers a fast and reliable infrastructure with extensive documentation and analytics.

Key Features:

Real-time logs
Advanced routing rules
Email validations
Webhooks
High delivery rates

Best For:
Tech-savvy developers and SaaS apps.

3. Elastic Email

Free Plan:

100 emails/day
Full API access
Contact management
Campaign builder

Why it’s great:
Elastic Email provides flexible pricing and powerful email API endpoints, ideal for small apps.

Key Features:

Easy SMTP integration
Webhooks and event tracking
Email templates
Real-time analytics
A/B testing

Best For:
Bootstrapped startups with limited email needs.

4. MailerSend

Free Plan:

3,000 emails/month
Up to 50 domains
Full API + SMTP relay
Real-time logs

Why it’s great:
MailerSend offers a modern UI and a developer-first approach with support for rich content and dynamic templates.

Key Features:

Drag & drop email builder
Email template engine
Detailed analytics
IP warm-up
Role-based permissions

Best For:
Growing teams and startups looking for collaborative workflows.

5. Amazon SES (Simple Email Service)

Free Plan (with AWS EC2):

62,000 emails/month (when sent from EC2)
SMTP and API access
Pay-as-you-go after free tier

Why it’s great:
Amazon SES is highly scalable and extremely affordable for high-volume apps. You only pay for what you use after the free tier.

Key Features:

Unmatched scalability
Trusted AWS infrastructure
Inbound email support
DKIM/SPF support
Bounce and complaint feedback

Best For:
Experienced developers, enterprise applications, and apps already using AWS.

Choosing the Right Free Transactional Email API

Not all APIs are created equal. Here’s how to choose the best fit:

1. Volume Needs

Start with how many emails you plan to send per day/month. Some tools are perfect for small projects, others are built to scale.

2. Ease of Integration

Look for RESTful APIs, SDKs, and clear documentation. Time-to-integration matters.

3. Deliverability

Choose providers with high inbox placement rates. Bounce and spam issues can hurt your brand.

4. Analytics

You need detailed logs and stats: opens, clicks, bounce rates, and delivery times.

5. Templates and Management

Drag-and-drop editors and reusable templates save hours of work.

How to Integrate a Free Transactional Email API (Step-by-Step)

Let’s walk through a basic integration example using MailerSend (similar for other platforms).

Step 1: Sign Up and Verify Domain

Create an account on MailerSend
Verify your sending domain with SPF/DKIM records

Step 2: Generate API Key

Go to “API Tokens”
Create a new token and save it securely

Step 3: Set Up API Call (Example using Python)

python

import requests

headers = {
“Authorization”: “Bearer YOUR_API_KEY”,
“Content-Type”: “application/json”
}

payload = {
“from”: {“email”: “you@yourdomain.com”},
“to”: [{“email”: “user@example.com”}],
“subject”: “Order Confirmation”,
“text”: “Your order has been received!”
}

response = requests.post(
“https://api.mailersend.com/v1/email”,
headers=headers,
json=payload
)

print(response.status_code)
print(response.json())

Step 4: Monitor Logs and Webhooks

Enable webhooks for delivery status
Monitor bounces and complaints

Best Practices for Sending Transactional Emails

To ensure smooth delivery and legal compliance, follow these tips:

✅ Use SPF, DKIM, and DMARC

Proper authentication reduces spam flagging.

✅ Keep Design Simple and Branded

Make it mobile-friendly and instantly recognizable.

✅ Include Essential Information

Always include contact info, links, and relevant details.

✅ Monitor Delivery and Feedback

Keep an eye on bounce rates, open rates, and errors.

✅ Avoid Marketing Content

Transactional emails must not be promotional to comply with anti-spam laws (CAN-SPAM, GDPR).

FAQ: Free Transactional Email APIs

Is it safe to use free email APIs?

Yes, as long as you’re using a reputable provider like Mailgun, Brevo, or AWS.

Can I upgrade when I grow?

Absolutely. Most services offer seamless upgrades once you outgrow the free tier.

Are there limitations with free plans?

Yes—mainly sending limits, API rate limits, and fewer advanced features like dedicated IPs.

Final Thoughts

Free transactional email APIs are a godsend for startups, indie developers, and small businesses. They deliver essential functionality without breaking the bank. By choosing the right provider and implementing best practices, you can ensure fast, secure, and reliable email delivery.

Whether you’re launching your first app or scaling a SaaS platform, transactional email APIs like MailerSend, Mailgun, Brevo, and Elastic Email give you a strong foundation—without the upfront costs.