Rails Action Mailer SMTP Setup

Action Mailer SMTP config

Configure production SMTP settings from environment variables:

config.action_mailer.delivery_method = :smtp
config.action_mailer.smtp_settings = {
  address: "smtp.postscale.io",
  port: 587,
  user_name: ENV.fetch("POSTSCALE_SMTP_USERNAME"),
  password: ENV.fetch("POSTSCALE_SMTP_PASSWORD"),
  authentication: :plain,
  enable_starttls_auto: true
}

Use a verified From domain:

class ApplicationMailer < ActionMailer::Base
  default from: "Acme <alerts@example.com>"
end

Queue mail

Use deliver_later for production transactional mail:

PasswordMailer.reset(user, token_id).deliver_later

Generate and store the token before enqueueing. Queue retries should resend the same token email, not generate a new token each time.

Migration from another provider

1. Publish Postscale DKIM, SPF, and return-path DNS records.
2. Keep the old provider's DNS records during transition.
3. Import bounces, complaints, and unsubscribes.
4. Change SMTP settings for one environment.
5. Test password reset, confirmation, and receipt flows.
6. Add webhook handling for final state.

If you are replacing Postmark, SendGrid, or Mailgun SDK calls, introduce a mail adapter rather than calling provider clients directly from models.

Webhook endpoint

Create a small controller that verifies signatures and stores events by provider event ID. Return 2xx only after durable acceptance.

Use webhook signature verification and webhook retries and idempotency as the implementation baseline.

References

• Rails Action Mailer Basics
• Rails Active Job Basics
• SMTP ports guide
• Transactional email bounces