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 provide

email-systems

Documentation