Ruby on Rails

Before you start

• Rails 6 or later

1Configure Action Mailer

# config/environments/development.rb
config.action_mailer.delivery_method = :smtp
config.action_mailer.perform_deliveries = true
config.action_mailer.raise_delivery_errors = true
config.action_mailer.smtp_settings = {
  address: 'smtp.mailclutch.com',
  port: 587,
  user_name: 'mc_0000000000000000',
  password: 'pw_0000000000000000',
  authentication: :plain,
  enable_starttls_auto: true
}

raise_delivery_errors is worth turning on here: without it a refused connection is swallowed and the inbox simply stays empty.

2Send a test message

From rails console:

ActionMailer::Base.mail(
  from: 'staging@example.com',
  to: 'anyone@example.com',
  subject: 'Sandbox check',
  body: 'Hello from Rails.'
).deliver_now

Watch it land

Open the sandbox and the message is there — rendered HTML, plain text, raw source, attachments, and the SPF, DKIM and DMARC verdicts. It updates live, so you can leave it open next to your terminal.

Nothing is ever delivered onward, whatever address you send to; claim the inbox with an account and it stays.

What usually goes wrong

• deliver_later needs a worker

  deliver_later hands the mail to Active Job. Either run the queue backend, or use deliver_now while you are testing.

• letter_opener and friends

  A gem that sets delivery_method to :letter_opener or :file in development overrides the block above. Comment it out for the environment you are pointing here.

• Credentials belong in ENV

  The snippet inlines the pair so you can paste it as is. For anything you commit, read it from ENV or Rails credentials instead.

Other stacks

The same four values in another dialect. Every guide below is filled in with the sandbox pair at the top of this page.