Email delivery infrastructure for SaaS app

Here’s a solid, practical overview of email delivery infrastructure for a SaaS app.

1) What you need

Most SaaS products need 2 email “classes”:

• Transactional email: signups, password resets, receipts, alerts, invite emails
• Marketing/product email: onboarding drips, newsletters, feature announcements

These should usually be handled differently for deliverability and compliance.

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2) Core architecture

A typical setup looks like this:

• App generates email events
• Queue / job system buffers sends
• Email service provider (ESP) sends mail
• Webhook processor ingests delivery events
• Bounce/complaint handling updates suppression lists
• Analytics/logging stores audit and delivery status

Basic flow

1. User triggers action in app
2. App enqueues email job
3. Worker renders template and sends via ESP
4. ESP returns message ID
5. ESP sends webhook events:
   • delivered
   • opened
   • clicked
   • bounced
   • complained
   • suppressed
6. Your system updates user/email status

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3) Recommended providers

For transactional email

• Postmark – excellent deliverability and simplicity
• Amazon SES – cheapest at scale, more setup
• SendGrid – common, broad feature set
• Mailgun – flexible, developer-friendly

For marketing email

• Customer.io
• Mailchimp
• SendGrid Marketing Campaigns
• Brevo (Sendinblue)

Many SaaS companies use:

• Postmark or SES for transactional
• Customer.io/Mailchimp for marketing

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4) Domain and authentication setup

This is critical for deliverability.

You should configure:

• SPF
• DKIM
• DMARC
• Optional: custom tracking domain

Best practice:

Use separate subdomains:

• mail.yourdomain.com for transactional
• news.yourdomain.com for marketing

This isolates reputation and reduces risk.

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5) Key infrastructure components

A. Email queue

Use a durable queue so sending is retryable and asynchronous.

Examples:

• Sidekiq / Redis
• Celery / RabbitMQ
• AWS SQS
• BullMQ

Benefits:

• avoids blocking user requests
• handles retries
• smooths spikes

B. Template rendering

Keep templates versioned and localized if needed.

Options:

• Handlebars/MJML
• React email
• Liquid
• Provider-native templates

C. Webhooks

Handle ESP webhooks securely:

• verify signatures
• deduplicate events
• store raw payloads
• process idempotently

D. Suppression management

Maintain lists for:

• hard bounces
• complaints
• unsubscribes
• invalid addresses

Never resend to suppressed recipients.

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6) Deliverability best practices

• Send from authenticated domains only
• Warm up new domains/IPs gradually
• Keep bounce and complaint rates low
• Use clear From names and reply-to
• Avoid spammy subject lines
• Include plain-text versions
• Always include unsubscribe links for marketing
• Segment and target emails
• Monitor inbox placement if volume is high

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7) Data model you’ll likely need

Minimal tables/entities:

• users
• email_messages
  • recipient
  • template
  • subject
  • status
  • provider_message_id
  • sent_at
• email_events
  • message_id
  • event_type
  • timestamp
  • raw_payload
• suppression_list
  • email
  • reason
  • source
  • created_at
• email_templates
  • key
  • version
  • locale
  • html/text content

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8) Observability

Track:

• send rate
• delivery rate
• bounce rate
• complaint rate
• open/click rates
• queue latency
• provider errors
• webhook processing failures

Set alerts for:

• spike in bounces
• spike in complaints
• provider outage
• queue backlog
• webhook failure rate

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9) Security and compliance

• Encrypt sensitive data at rest
• Limit who can send mail
• Verify webhooks
• Store audit logs
• Support unsubscribe and data deletion
• Respect GDPR/CCPA where applicable
• Don’t mix transactional and marketing consent unintentionally

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10) A good default stack

If you want a simple, robust SaaS setup:

• Transactional: Postmark
• Marketing: Customer.io or Mailchimp
• Queue: Sidekiq / SQS
• Templates: MJML or React Email
• Events: provider webhooks into your backend
• Analytics: basic internal dashboard + error alerts

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11) If you’re just starting

Start with:

1. One transactional ESP
2. SPF/DKIM/DMARC
3. Queue-based sending
4. Webhook ingestion
5. Suppression lists
6. Basic monitoring

Then add marketing automation later.

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If you want, I can also provide:

• a reference architecture diagram
• a cost comparison of SES vs SendGrid vs Postmark
• or a production-ready email sending flow in code for Node/Python/Rails.