8 Best Free Transactional Email APIs for Ruby (2026), Tested

criteria

• Monthly send volume
• Daily caps
• Feature limitations
• Ruby SDK or SMTP support

1. 01

   Mailjet

   Transactional Marketing

   6,000/mo capped at 200/day. Permanent and useful for steady low-volume sends.

2. 02

   Loops

   Marketing Transactional

   Unlimited emails on the Free plan within a 1,000-contact ceiling. Different model: optimal when your contact list grows slowly but your volume is high.

3. 03

   Brevo

   Transactional Marketing

   300/day permanent. Best for low daily volumes that do not spike on launch day.

4. 04

   Mailtrap

   Transactional Testing

   4,000/mo permanent on the sending side, plus a free testing tier.

5. 05

   Resend

   Transactional

   3,000/mo permanent on a single domain.

6. 06

   MailerSend

   Transactional

   3,000/mo permanent.

7. 07

   Amazon SES

   Transactional

   New accounts get up to $200 in AWS credits for six months. The old 62,000/mo-from-EC2 allowance is gone.

8. 08

   SMTP2GO

   Transactional

   1,000/mo permanent, no daily cap.

Send your first email from Ruby

Minimal send calls on the free tier, in ranking order. Swap the from address for a domain you have verified with the provider.

require "resend"

Resend.api_key = ENV["RESEND_API_KEY"]
Resend::Emails.send({
  from: "you@yourdomain.com",
  to: ["user@example.com"],
  subject: "Hello",
  html: "<p>It works.</p>",
})

require "aws-sdk-sesv2"

client = Aws::SESV2::Client.new(region: "us-east-1")
client.send_email({
  from_email_address: "you@yourdomain.com",
  destination: { to_addresses: ["user@example.com"] },
  content: { simple: {
    subject: { data: "Hello" },
    body: { text: { data: "It works." } },
  } },
})

require "net/smtp"

message = <<~MSG
  From: you@yourdomain.com
  To: user@example.com
  Subject: Hello

  It works.
MSG

Net::SMTP.start("mail.smtp2go.com", 587,
                user: ENV["SMTP_USER"], secret: ENV["SMTP_PASS"],
                authtype: :plain, starttls: :always) do |smtp|
  smtp.send_message(message, "you@yourdomain.com", "user@example.com")
end

All 8 compared

other languages

• Python
• Node.js
• Go
• PHP
• Ruby SDK guide

reading this as developers picking email infrastructure

The question here is which one a backend engineer would rather operate. That means SDK depth in the language already in use, whether a retry can safely be replayed, how much the event log tells you when a customer says the email never arrived, and whether the pricing curve stays sane as volume grows.

Applied to free Ruby email sending, that means weighing developer experience, SDK breadth, idempotency keys, and operating track record ahead of the rest, against password resets, receipts, and magic links shipped from application code.