email-systems

Email Systems

Email has the highest ROI of any marketing channel. $36 for every $1 spent. Yet most startups treat it as an afterthought - bulk blasts, no personalization, landing in spam folders.

This skill covers transactional email that works, marketing automation that converts, deliverability that reaches inboxes, and the infrastructure decisions that scale.

Principles

• Transactional vs Marketing separation | Description: Transactional emails (password reset, receipts) need 100% delivery.

Marketing emails (newsletters, promos) have lower priority. Use separate IP addresses and providers to protect transactional deliverability. | Examples: Good: Password resets via Postmark, marketing via ConvertKit | Bad: All emails through one SendGrid account

• Permission is everything | Description: Only email people who asked to hear from you. Double opt-in for marketing.

Easy unsubscribe. Clean your list ruthlessly. Bad lists destroy deliverability. | Examples: Good: Confirmed subscription + one-click unsubscribe | Bad: Scraped email list, hidden unsubscribe, bought contacts

• Deliverability is infrastructure | Description: SPF, DKIM, DMARC are not optional. Warm up new IPs. Monitor bounce rates.

Deliverability is earned through technical setup and good behavior. | Examples: Good: All DNS records configured, dedicated IP warmed for 4 weeks | Bad: Using free tier shared IP, no authentication records

• One email, one goal | Description: Each email should have exactly one purpose and one CTA. Multiple asks

means nothing gets clicked. Clear single action. | Examples: Good: "Click here to verify your email" (one button) | Bad: "Verify email, check out our blog, follow us on Twitter, refer a friend..."

• Timing and frequency matter | Description: Wrong time = low open rates. Too frequent = unsubscribes. Let users

set preferences. Test send times. Respect inbox fatigue. | Examples: Good: Weekly digest on Tuesday 10am user's timezone, preference center | Bad: Daily emails at random times, no way to reduce frequency

Patterns

Transactional Email Queue

Queue all transactional emails with retry logic and monitoring

When to use: Sending any critical email (password reset, receipts, confirmations)

// Don't block request on email send await queue.add('email', { template: 'password-reset', to: user.email, data: { resetToken, expiresAt } }, { attempts: 3, backoff: { type: 'exponential', delay: 2000 } });

Email Event Tracking

Track delivery, opens, clicks, bounces, and complaints

When to use: Any email campaign or transactional flow

Track lifecycle:

• Queued: Email entered system
• Sent: Handed to provider
• Delivered: Reached inbox
• Opened: Recipient viewed
• Clicked: Recipient engaged
• Bounced: Permanent failure
• Complained: Marked as spam

Template Versioning

Version email templates for rollback and A/B testing

When to use: Changing production email templates

templates/ password-reset/ v1.tsx (current) v2.tsx (testing 10%) v1-deprecated.tsx (archived)

Deploy new version gradually

Monitor metrics before full rollout

Bounce Handling State Machine

Automatically handle bounces to protect sender reputation

When to use: Processing bounce and complaint webhooks

switch (bounceType) { case 'hard': await markEmailInvalid(email); break; case 'soft': await incrementBounceCount(email); if (count >= 3) await markEmailInvalid(email); break; case 'complaint': await unsubscribeImmediately(email); break; }

React Email Components

Build emails with reusable React components

When to use: Creating email templates

import { Button, Html } from '@react-email/components';

export default function WelcomeEmail({ userName }) { return ( <Html> <h1>Welcome {userName}!</h1> <Button href="https://app.com/start"> Get Started </Button> </Html> ); }

Preference Center

Let users control email frequency and topics

When to use: Building marketing or notification systems

Preferences: ☑ Product updates (weekly) ☑ New features (monthly) ☐ Marketing promotions ☑ Account notifications (always)

Respect preferences in all sends

Required for GDPR compliance

Sharp Edges

Missing SPF, DKIM, or DMARC records

Severity: CRITICAL

Situation: Sending emails without authentication. Emails going to spam folder. Low open rates. No idea why. Turns out DNS records were never set up.

Symptoms:

• Emails going to spam
• Low deliverability rates
• mail-tester.com score below 8
• No DMARC reports received

Why this breaks: Email authentication (SPF, DKIM, DMARC) tells receiving servers you're legit. Without them, you look like a spammer. Modern email providers increasingly require all three.

Recommended fix:

Required DNS records:

SPF (Sender Policy Framework)

TXT record: v=spf1 include:_spf.google.com include:sendgrid.net ~all

DKIM (DomainKeys Identified Mail)

TXT record provided by your email provider Adds cryptographic signature to emails

DMARC (Domain-based Message Authentication)

TXT record: v=DMARC1; p=quarantine; rua=mailto:dmarc@yourdomain.com

Verify setup:

• Send test email to mail-tester.com
• Check MXToolbox for record validation
• Monitor DMARC reports

Using shared IP for transactional email

Severity: HIGH

Situation: Password resets going to spam. Using free tier of email provider. Some other customer on your shared IP got flagged for spam. Your reputation is ruined by association.

Symptoms:

• Transactional emails in spam
• Inconsistent delivery
• Using same provider for marketing and transactional

Why this breaks: Shared IPs share reputation. One bad actor affects everyone. For critical transactional email, you need your own IP or a provider with strict shared IP policies.

Recommended fix:

Transactional email strategy:

Option 1: Dedicated IP (high volume)

• Get dedicated IP from your provider
• Warm it up slowly (start with 100/day)
• Maintain consistent volume

Option 2: Transactional-only provider

• Postmark (very strict, great reputation)
• Includes shared pool with high standards

Separate concerns:

• Transactional: Postmark or Resend
• Marketing: ConvertKit or Customer.io
• Never mix marketing and transactional

Not processing bounce notifications

Severity: HIGH

Situation: Emailing same dead addresses over and over. Bounce rate climbing. Email provider threatening to suspend account. List is 40% dead.

Symptoms:

• Bounce rate above 2%
• No webhook handlers for bounces
• Same emails failing repeatedly

Why this breaks: Bounces damage sender reputation. Email providers track bounce rates. Above 2% and you start looking like a spammer. Dead addresses must be removed immediately.

Recommended fix:

Bounce handling requirements:

Hard bounces:

Remove immediately on first occurrence Invalid address, domain doesn't exist

Soft bounces:

Retry 3 times over 72 hours After 3 failures, treat as hard bounce

Implementation:

// Webhook handler for bounces
app.post('/webhooks/email', (req, res) => {
  const event = req.body;
  if (event.type === 'bounce') {
    await markEmailInvalid(event.email);
    await removeFromAllLists(event.email);
  }
});

Monitor:

Track bounce rate by campaign Alert if bounce rate exceeds 1%

Missing or hidden unsubscribe link

Severity: CRITICAL

Situation: Users marking as spam because they cannot unsubscribe. Spam complaints rising. CAN-SPAM violation. Email provider suspends account.

Symptoms:

• Hidden unsubscribe links
• Multi-step unsubscribe process
• No List-Unsubscribe header
• High spam complaint rate

Why this breaks: Users who cannot unsubscribe will mark as spam. Spam complaints hurt reputation more than unsubscribes. Also it is literally illegal. CAN-SPAM, GDPR all require clear unsubscribe.

Recommended fix:

Unsubscribe requirements:

Visible:

• Above the fold in email footer
• Clear text, not