Ruby

send.rb

require "net/http"
require "json"
require "uri"

class SpacePost
  API = URI("https://api.spacepost.dev")

  class Error < StandardError
    attr_reader :status_code, :name
    def initialize(body, status)
      @status_code = status
      @name = body["name"]
      super("#{body["name"]}: #{body["message"]}")
    end
  end

  def initialize(api_key = ENV.fetch("SPACEPOST_API_KEY"))
    @api_key = api_key
  end

  def send_email(email, idempotency_key: nil)
    req = Net::HTTP::Post.new("/emails")
    req["Authorization"] = "Bearer #{@api_key}"
    req["Content-Type"] = "application/json"
    req["Idempotency-Key"] = idempotency_key if idempotency_key
    req.body = JSON.generate(email)

    res = Net::HTTP.start(API.host, API.port, use_ssl: true, read_timeout: 15) { |http| http.request(req) }
    body = JSON.parse(res.body)
    raise Error.new(body, res.code.to_i) unless res.is_a?(Net::HTTPSuccess)
    body # {"id" => "..."}
  end
end

puts SpacePost.new.send_email(
  from: "Acme <hello@acme.com>",
  to: ["delivered@test.spacepost.dev"],
  subject: "Hello from Ruby",
  html: "<p>It works.</p>"
)

¿Usas Rails? El relé SMTP funciona con Action Mailer sin cambios.