The Best Email APIs for Developers in 2025

How We Evaluated These APIs

We tested each email API by building the same application: a SaaS product that sends transactional emails (welcome, password reset, invoice), marketing campaigns (weekly newsletter), and automated sequences (onboarding drip). We evaluated developer experience (time to first email sent), documentation quality, SDK design, deliverability rates, pricing at various volume tiers, and support responsiveness. All tests were conducted between January and April 2025.

Our evaluation criteria weighted developer experience most heavily because an API you struggle to integrate is an API you will eventually replace. We also tracked deliverability across Gmail, Outlook, and Yahoo over a 30-day period for each provider, sending identical content from properly authenticated domains.

Resend

Resend has rapidly become the default choice for developers building with modern frameworks. Their API is clean, their documentation is excellent, and their React Email framework has fundamentally changed how developers think about email templates. If you are building a Next.js or React application, Resend feels like a natural extension of your stack.

import { Resend } from "resend";

const resend = new Resend(process.env.RESEND_API_KEY);

await resend.emails.send({
  from: "hello@yourdomain.com",
  to: "user@example.com",
  subject: "Welcome to our platform",
  react: WelcomeEmail({ username: "Alice" })
});

Pros: Beautiful developer experience. React Email integration is a game-changer. Generous free tier (100 emails/day). Fast, responsive team. Excellent TypeScript support.

Cons: Relatively young platform with a smaller feature set than established players. Marketing/campaign features are still maturing. No built-in sequence builder. Deliverability monitoring tools are basic compared to Postmark.

Best for: Transactional email in React/Next.js applications. Startups that want a modern, developer-first experience.

SendGrid

SendGrid (owned by Twilio) is the incumbent. It handles over 100 billion emails per month and offers the most comprehensive feature set of any email API. The platform covers transactional email, marketing campaigns, contact management, and analytics. It is the Swiss Army knife of email APIs.

import sgMail from "@sendgrid/mail";

sgMail.setApiKey(process.env.SENDGRID_API_KEY);

await sgMail.send({
  to: "user@example.com",
  from: "hello@yourdomain.com",
  subject: "Welcome to our platform",
  text: "Welcome aboard!",
  html: "<h1>Welcome aboard!</h1>"
});

Pros: Massive scale and proven reliability. Comprehensive feature set. Strong deliverability at volume. Good documentation. Wide language support for SDKs.

Cons: Developer experience feels dated compared to newer alternatives. The dashboard is cluttered and confusing. Support quality varies significantly by plan tier. Pricing can get expensive at scale. The SDK API design shows its age.

Best for: High-volume senders who need a battle-tested platform. Enterprise teams with existing Twilio relationships.

Postmark

Postmark is laser-focused on transactional email deliverability. They deliberately separate transactional and marketing email into different products (Postmark for transactional, DMARC Digests for monitoring) because mixing the two degrades deliverability. This opinionated approach pays off: Postmark consistently reports the fastest delivery times and highest inbox placement rates in the industry.

import { ServerClient } from "postmark";

const client = new ServerClient(process.env.POSTMARK_API_KEY);

await client.sendEmail({
  From: "hello@yourdomain.com",
  To: "user@example.com",
  Subject: "Welcome to our platform",
  HtmlBody: "<h1>Welcome!</h1>",
  TextBody: "Welcome!",
  MessageStream: "outbound"
});

Pros: Industry-leading transactional deliverability. Excellent delivery speed (median under 1 second). Outstanding documentation and transparency. Built-in bounce and spam complaint tracking. DMARC monitoring tools.

Cons: Not designed for marketing campaigns. Pricing is higher than alternatives at volume. Template system is functional but not as elegant as React Email. No built-in sequence or automation features.

Best for: Teams where transactional email deliverability is mission-critical (password resets, 2FA, receipts).

Mailgun

Mailgun (owned by Sinch/Pathwire) offers a solid, full-featured email API with particular strengths in email validation and routing. Their API design is REST-ful and well-structured, and they offer some unique features like inbound email parsing and advanced routing rules that are harder to find elsewhere.

import formData from "form-data";
import Mailgun from "mailgun.js";

const mg = new Mailgun(formData).client({
  username: "api",
  key: process.env.MAILGUN_API_KEY
});

await mg.messages.create("yourdomain.com", {
  from: "hello@yourdomain.com",
  to: "user@example.com",
  subject: "Welcome to our platform",
  html: "<h1>Welcome!</h1>"
});

Pros: Strong email validation API. Good inbound email processing. Flexible routing rules. Reasonable pricing. EU region available for GDPR compliance.

Cons: SDK design is clunky (the form-data dependency is a pain point). Documentation has gaps. Dashboard UX needs work. Deliverability is good but not best-in-class. The platform has changed ownership multiple times, creating uncertainty.

Best for: Teams that need inbound email processing or advanced routing alongside outbound sending.

Brew

Brew is the newest entrant in this comparison and takes a distinctly different approach. While the other APIs are primarily sending infrastructure, Brew combines sending with AI-powered campaign creation, sequence building, and deliverability optimization in a single platform. It is designed for teams that want to manage their entire email program through an API, not just the sending layer.

import { Brew } from "@brew/sdk";

const brew = new Brew({ apiKey: process.env.BREW_API_KEY });

// Send a single email
await brew.emails.send({
  from: "hello@yourdomain.com",
  to: "user@example.com",
  subject: "Welcome to our platform",
  template: "welcome",
  data: { username: "Alice" }
});

// Or create an entire sequence
await brew.sequences.create({
  name: "Onboarding",
  trigger: { event: "user.signup" },
  steps: [
    { delay: "0m", template: "welcome" },
    { delay: "24h", template: "getting-started" },
    { delay: "72h", template: "advanced-features" }
  ]
});

Pros: AI-powered content generation and optimization. Built-in sequence builder with conditional logic. Self-improving deliverability engine. Clean, modern SDK. Integrated analytics with conversion tracking. Competitive pricing.

Cons: Newer platform with a smaller track record. Fewer third-party integrations than SendGrid. Community and ecosystem are still growing. Some advanced features are only available on higher-tier plans.

Best for: Teams that want an all-in-one email platform with AI capabilities. Startups and mid-stage companies building sophisticated email programs without dedicated email engineers.

Comparison Summary and Recommendations

If you are choosing an email API in 2025, here is the decision framework: Choose Resend if you are building a React/Next.js app and primarily need transactional email. Choose SendGrid if you need a proven platform at massive scale. Choose Postmark if transactional deliverability is your top priority and you do not need marketing features. Choose Mailgun if you need inbound email processing or advanced routing. Choose Brew if you want to consolidate sending, sequences, and AI-powered optimization into a single platform.

The email API market in 2025 is mature enough that there are no truly bad options on this list. The differences come down to your specific needs, your team\'s technical preferences, and how much of your email program you want the platform to handle versus building yourself. Our recommendation for most startups is to start with Resend or Brew for their developer experience, and evaluate a move to SendGrid or Postmark only if you hit specific scaling or deliverability requirements that demand it.