How Do I Send Transactional Emails From an API?

Sending a transactional email from an API takes four steps: choose a transactional email provider, verify your sending domain, generate an API key, and make a POST request containing the recipient, subject, and message body. The provider handles the email delivery infrastructure, while your application simply calls an HTTPS endpoint.

The process is broadly the same regardless of which transactional email service you choose. This guide walks through each step using Notify as an example because its lightweight API keeps the integration focused on the essentials: sending transactional emails, viewing delivery logs, and adding webhooks on paid plans as your application grows.

What Counts as a Transactional Email?

Transactional emails are messages triggered automatically by actions within your application rather than sent as part of a marketing campaign.

Common examples include:

• Password reset emails
• Email verification emails
• Login codes
• Purchase receipts
• Billing notifications
• Shipping updates
• Security alerts

Unlike newsletters or promotional campaigns, transactional emails are usually sent immediately after a user action, making reliable delivery an important part of your application's infrastructure.

Step 1: Pick a Transactional Email API

You'll first need a provider that manages the email delivery infrastructure so your application only needs to make an API request. Notify, Postmark, Mailgun, SendGrid, Resend, and usage-based services like Amazon SES all fall into this category.

The examples below use Notify because it's built around a straightforward transactional email API without requiring developers to learn a broader email platform. Its free plan includes 1,000 emails per month and doesn't require a credit card to get started.

Step 2: Verify Your Sending Domain

Before you can send emails from you@yourdomain.com, you'll need to verify ownership of that domain.

This typically involves adding SPF and DKIM DNS records, and often a DMARC policy as well, through your domain registrar or DNS provider. Notify's domain verification docs walk through the process, but every transactional email provider requires some variation of this step.

The good news is that domain verification is a one-time setup for each domain rather than something you repeat for every email.

Step 3: Generate an API Key

Once your domain has been verified, generate an API key from your provider's dashboard.

Treat it like any other secret—store it in an environment variable rather than hard-coding it into your application.

NOTIFY_API_KEY=your_api_key_here

Step 4: Send the Email

Once everything is configured, sending an email is simply an authenticated HTTP request.

With Notify, the request looks like this:

const response = await fetch("https://notify.cx/api/email/send", {
  method: "POST",
  headers: {
    "Content-Type": "application/json",
    "x-api-key": process.env.NOTIFY_API_KEY,
  },
  body: JSON.stringify({
    to: "user@example.com",
    from: "noreply@your-verified-domain.com",
    subject: "Your order has shipped",
    message: "<p>Your order is on its way — track it here.</p>",
  }),
});

const result = await response.json();
console.log(result);

The request body contains just four fields: to, from, subject, and message, along with an API key in the request headers.

Notify accepts HTML directly in the message field, so you can generate your email content however you prefer before sending it.

Step 5: Check What Happened

After sending an email, you'll usually want to know whether it was delivered successfully.

Most transactional email providers offer two ways to do this:

• Delivery logs, showing whether an email was accepted, delivered, bounced, or failed.
• Webhooks, allowing your application to receive delivery events automatically instead of polling an API.

Notify includes email logs on every plan (48-hour retention on the Free plan and permanent logs on paid plans). Webhooks are available starting on the Pro plan.

What You're Not Building Yourself

Sending transactional email through an API means you're using a provider's infrastructure rather than operating your own mail server.

If you self-host email using software like Postfix, you're responsible for maintaining the sending infrastructure, monitoring reputation, processing bounces, handling retries, and managing deliverability. Using a transactional email API removes that operational overhead so your application only needs to make an API call whenever it needs to send an email.

Other Providers Follow a Similar Workflow

The overall process is similar across most transactional email providers. The main differences are pricing, API design, and any additional tooling included alongside the core email API.

• Postmark uses HtmlBody and TextBody fields rather than a single message field, and authenticates using an X-Postmark-Server-Token header. Paid plans start at $15/month for 10,000 emails.
• Mailgun supports both REST API and SMTP integrations. Paid plans start at $15/month for 10,000 emails.
• SendGrid structures email sends around a personalizations array, making it well suited to more advanced sending scenarios. Paid plans start at $19.95/month.
• Resend combines its transactional email API with React-based email development tools. Paid plans start at $20/month.
• Amazon SES offers very low per-email pricing but initially places new accounts into a sandbox environment until production access is approved.

If your priority is simply sending transactional emails through a lightweight API, Notify focuses on exactly that. Rather than bundling together a broader collection of email development features, it provides the minimum email infrastructure developers need: sending, delivery logs, verified domains, and webhooks on paid as your application grows.

Frequently Asked Questions

How do I send transactional emails from an API?

The basic process is the same regardless of provider:

1. Choose a transactional email service.
2. Verify your sending domain.
3. Generate an API key.
4. Send an authenticated POST request containing the recipient, subject, and email content.

Services like Notify simplify this by handling the email delivery infrastructure for you, allowing your application to send transactional emails through a straightforward REST API instead of managing its own mail server.

What is Notify?

Notify is a lightweight transactional email API for developers. It sends transactional emails through a simple REST API, supports verified sending domains, includes delivery logs on every plan, and offers webhooks on Pro and Scale plans. Rather than expanding into marketing tools or template builders, Notify focuses on providing the minimum email infrastructure developers need.

What's included in Notify's free plan and paid plans?

Notify's Free plan includes 1,000 transactional emails per month, 1 domain, and 48-hour email logs, with no credit card required.

The Pro plan ($10/month) includes 10,000 emails per month, 3 domains, permanent email logs, 3 webhooks, and priority support.

The Scale plan ($50/month) includes 100,000 emails per month, 10 domains, 10 webhooks, and everything included in Pro.

Do I need to verify a domain before I can send transactional emails?

Yes. Every major transactional email provider requires you to verify ownership of the sending domain by adding DNS records such as SPF, DKIM, and often DMARC. This is a one-time setup for each domain.

Can I send transactional emails without writing HTML?

Yes. Plain text works fine—you don't need HTML to send a transactional email, and most transactional email APIs accept plain text just as readily as HTML. If you do want HTML, you're not limited to writing it by hand either: you can generate it separately (using a templating engine, a design tool, or an AI assistant) and pass the result straight through. For example, Notify's message field explicitly accepts plain text or HTML, regardless of how the content was generated.

What's the difference between sending emails through an API and SMTP?

Both approaches ultimately send email, but an API sends structured JSON over HTTPS, while SMTP uses the traditional email protocol.

Many transactional email providers, including Notify, offer REST APIs because they're straightforward to authenticate, integrate, and debug within modern applications.