Mailgun vs SMTPfast: Developer Email API Comparison

Old Guard vs New Blood

Mailgun was one of the first email APIs built for developers. It has grown into a full platform with email validation, inbox placement testing, inbound routing, and more. SMTPfast stays focused on product email: transactional sends, SMTP relay, broadcasts, forms, contacts, suppressions, and live debugging.

Feature Comparison

Pricing

Mailgun's pricing has more moving parts than SMTPfast. Basic starts at $15/month for 10K emails, Foundation starts at $35/month for 50K, and Scale starts at $90/month for 100K. Dedicated IP access depends on volume and plan, so you need to read carefully to understand what you are actually paying for.

Where Mailgun Wins

Email validation. Mailgun has a built-in email validation API that checks whether addresses are deliverable before you send. This is a paid add-on, but it is convenient to have it in the same platform.

Mature SMTP relay. If you have applications that send via SMTP (WordPress, legacy systems, CRM tools), Mailgun has had this workflow for a long time. SMTPfast supports SMTP too, but Mailgun is the older and broader platform.

Routing and forwarding. Mailgun can receive email and route it to different endpoints based on rules. Useful for apps that need to process incoming mail.

Mailing lists. Built-in mailing list management if you need it.

Inbox placement testing. Mailgun's "Inbox Placement" tool (Scale plan) lets you test where your email lands before you send to real users.

Where SMTPfast Wins

Developer experience. SMTPfast has the cleanest API in the space. Send an email with a single fetch() call, no SDK needed.

await fetch("https://smtpfa.st/api/v1/emails", {
  method: "POST",
  headers: {
    Authorization: `Bearer ${process.env.SMTPFAST_API_KEY}`,
    "Content-Type": "application/json",
  },
  body: JSON.stringify({
    from: "App <[email protected]>",
    to: "[email protected]",
    subject: "Your receipt",
    html: receiptHtml,
  }),
});

Pricing clarity. SMTPfast pricing is simple: Free tier, then Starter, Growth, and Scale. Flat monthly prices, clear monthly allowances, and optional prepaid credits for extra volume.

Setup speed. With Mailgun, you need to verify your domain, set up sending credentials, and click through their dashboard to find the right API endpoint (US vs EU region). SMTPfast: add your domain, grab an API key, send.

No SDK required. Mailgun's raw API has quirks. Their sending endpoint uses multipart/form-data by default, which is unusual for a modern REST API.

# Mailgun uses form data, not JSON
curl -s --user "api:YOUR_MAILGUN_KEY" \
  https://api.mailgun.net/v3/YOUR_DOMAIN/messages \
  -F from="[email protected]" \
  -F to="[email protected]" \
  -F subject="Your receipt" \
  -F html="<h1>Your receipt</h1>"

# SMTPfast uses JSON
curl -X POST https://smtpfa.st/api/v1/emails \
  -H "Authorization: Bearer sf_your_api_key" \
  -H "Content-Type: application/json" \
  -d '{"from":"[email protected]","to":"[email protected]","subject":"Your receipt","html":"<h1>Your receipt</h1>"}'

Resend compatibility. Migrating from Resend to SMTPfast is a two-line change. Migrating from Resend to Mailgun means rewriting your integration.

API Design Philosophy

Mailgun was designed in an era when REST APIs commonly used form-encoded data. Their API reflects that. It works, but it feels dated compared to modern JSON-first APIs.

SMTPfast was designed after Resend showed what a clean email API looks like. Standard Bearer auth, JSON payloads, lowercase field names, and predictable responses.

Who Should Use What?

Choose Mailgun if:

• You need SMTP relay for legacy systems
• Email validation is important to your workflow
• You want routing and mailing list features
• You are already on Mailgun and it works for you

Choose SMTPfast if:

• You want the simplest, most modern API
• You are building a new project and want fast setup
• Pricing transparency matters to you
• You are migrating from Resend

The Bottom Line

Mailgun is a capable platform with a lot of features. If you need those features, it is a solid choice. But if you just need to send transactional emails from your app with a clean API and fair pricing, SMTPfast gets you there faster with less overhead.