Rails

config/environments/production.rb

config.action_mailer.delivery_method = :smtp
config.action_mailer.perform_deliveries = true
config.action_mailer.raise_delivery_errors = true
config.action_mailer.default_url_options = { host: "acme.com", protocol: "https" }

config.action_mailer.smtp_settings = {
  address: "smtp.spacepost.dev",
  port: 25976,
  user_name: "spacepost",
  password: ENV.fetch("SPACEPOST_API_KEY"),
  authentication: :plain,
  enable_starttls_auto: true
}

enable_starttls_auto: true faz o upgrade da conexão com STARTTLS antes do login. Não defina ssl: true nem tls: true: o TLS implícito (porta 465) ainda não é oferecido.

app/mailers/application_mailer.rb

class ApplicationMailer < ActionMailer::Base
  default from: "Acme <hello@acme.com>"
  layout "mailer"
end

Adicione tags ou um agendamento por e-mail:

class UserMailer < ApplicationMailer
  def welcome(user)
    headers["X-SpacePost-Tags"] = "category=welcome"
    mail(to: user.email, subject: "Welcome to Acme")
  end
end

Use o Active Job (deliver_later) para que uma chamada SMTP lenta nunca bloqueie uma requisição web.

bin/rails runner 'ActionMailer::Base.mail(from: "hello@acme.com", to: "delivered@test.spacepost.dev", subject: "Test", body: "It works").deliver_now'