I'm building a subscription app. What's a good way to send billing emails?

A good pattern is:

1. Use your app to trigger events

   • Emit billing events like invoice.created, payment.succeeded, payment.failed, subscription.canceled, card_expiring_soon.
   • Keep the email content tied to those events, not to manual admin actions.

2. Send via a transactional email service

   • Common choices: SendGrid, Postmark, Mailgun, Amazon SES, Resend.
   • These handle deliverability, bounce tracking, suppression lists, and retries better than sending directly from your app server.

3. Make emails template-driven

   • Create separate templates for:
     • receipt / invoice
     • payment failed
     • card expiring soon
     • renewal reminder
     • subscription canceled
   • Use variables for customer name, plan, amount, renewal date, invoice link, etc.

4. Send asynchronously

   • Put email jobs on a queue (e.g., Sidekiq, Celery, BullMQ, SQS).
   • This prevents your billing flow from slowing down or failing because of email issues.

5. Make them reliable and idempotent

   • If the same billing event is retried, don’t send duplicate emails.
   • Store an event ID or dedupe key like invoice_123_receipt_sent.

6. Include compliance basics

   • Use a verified sending domain with SPF, DKIM, and DMARC.
   • Use a clear from address like billing@yourapp.com.
   • For promotional emails, include unsubscribe; for strictly transactional billing emails, usually separate them from marketing lists.

7. Provide self-serve access

   • In every billing email, include links to:
     • view invoice
     • update payment method
     • manage subscription
     • contact support

8. Track delivery and failures

   • Log sent emails and webhook events for bounces, complaints, and delivery.
   • Surface failed-payment notifications in-app too, not only by email.

If you want, I can suggest a simple architecture diagram or a concrete implementation using your stack (e.g. Node, Python, Rails).