email-systems

Included with Lifetime

$97 forever

Transactional email (Resend, SendGrid, SES), templates (React Email, MJML), deliverability (SPF/DKIM/DMARC), and inboxing best practices. Use when building email infrastructure, designing templates, or troubleshooting deliverability.

Web Dev

What this skill does


# Email Systems

## Overview

This skill covers building reliable email systems for web applications, including transactional email sending, template design, deliverability optimization, and inbox placement. It addresses integration with email service providers (Resend, AWS SES, SendGrid, Postmark), building responsive HTML email templates with React Email and MJML, configuring DNS records for deliverability (SPF, DKIM, DMARC), managing email types (transactional, notification, marketing), queue management, and bounce/complaint handling.

Use this skill when sending welcome emails, password resets, order confirmations, notification digests, marketing campaigns, or any system-generated email. Also use when debugging deliverability issues or migrating between email providers.

---

## Core Principles

1. **Transactional and marketing are different** - Transactional emails (password reset, receipt) must arrive instantly and reliably. Marketing emails (newsletter, promo) can be batched and should have unsubscribe links. Never mix them on the same sending domain.
2. **HTML email is not web development** - Email clients render HTML from 2004. No flexbox, no grid, no modern CSS. Use tables for layout, inline styles, and test across clients. React Email and MJML abstract this pain.
3. **Deliverability is earned** - SPF, DKIM, and DMARC are table stakes, not guarantees. Maintain low bounce rates (< 2%), low complaint rates (< 0.1%), and warm up new sending domains gradually.
4. **Queue everything** - Never send email synchronously in a request handler. Queue email sends to avoid blocking user requests and to enable retry on failure.
5. **Test before sending** - Use Mailtrap or Ethereal in development, preview in multiple clients (Litmus, Email on Acid), and verify every link works.

---

## Key Patterns

### Pattern 1: React Email Templates with Resend

**When to use:** Building type-safe, component-based email templates with modern DX and reliable delivery.

**Implementation:**

```tsx
// emails/welcome.tsx - React Email template
import {
  Html,
  Head,
  Body,
  Container,
  Section,
  Text,
  Button,
  Img,
  Hr,
  Link,
  Preview,
} from "@react-email/components";

interface WelcomeEmailProps {
  userName: string;
  loginUrl: string;
  guideUrl: string;
}

export function WelcomeEmail({ userName, loginUrl, guideUrl }: WelcomeEmailProps) {
  return (
    <Html lang="en">
      <Head />
      <Preview>Welcome to MyApp, {userName}! Here&apos;s how to get started.</Preview>
      <Body style={styles.body}>
        <Container style={styles.container}>
          <Img
            src="https://myapp.com/logo.png"
            width={120}
            height={36}
            alt="MyApp"
          />

          <Section style={styles.section}>
            <Text style={styles.heading}>Welcome, {userName}!</Text>
            <Text style={styles.text}>
              Thanks for signing up. Your account is ready to go.
              Here are three things to get you started:
            </Text>

            <Text style={styles.listItem}>
              <strong>1. Create your first project</strong> - Click "New Project" on your dashboard.
            </Text>
            <Text style={styles.listItem}>
              <strong>2. Invite your team</strong> - Share your workspace with colleagues.
            </Text>
            <Text style={styles.listItem}>
              <strong>3. Explore the guide</strong> - Learn tips and best practices.
            </Text>

            <Section style={styles.buttonContainer}>
              <Button style={styles.button} href={loginUrl}>
                Go to Dashboard
              </Button>
            </Section>
          </Section>

          <Hr style={styles.hr} />

          <Section style={styles.footer}>
            <Text style={styles.footerText}>
              Need help? Reply to this email or visit our{" "}
              <Link href={guideUrl} style={styles.link}>help center</Link>.
            </Text>
            <Text style={styles.footerText}>
              MyApp, Inc. | 123 Street, City, ST 12345
            </Text>
          </Section>
        </Container>
      </Body>
    </Html>
  );
}

const styles = {
  body: {
    backgroundColor: "#f6f9fc",
    fontFamily: '-apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif',
  },
  container: {
    backgroundColor: "#ffffff",
    margin: "0 auto",
    padding: "20px 0 48px",
    maxWidth: "600px",
    borderRadius: "8px",
  },
  section: { padding: "0 48px" },
  heading: { fontSize: "24px", fontWeight: "bold" as const, marginBottom: "16px" },
  text: { fontSize: "16px", lineHeight: "26px", color: "#404040" },
  listItem: { fontSize: "15px", lineHeight: "24px", color: "#404040", marginBottom: "8px" },
  buttonContainer: { textAlign: "center" as const, marginTop: "24px", marginBottom: "24px" },
  button: {
    backgroundColor: "#0066ff",
    borderRadius: "6px",
    color: "#ffffff",
    fontSize: "16px",
    fontWeight: "bold" as const,
    textDecoration: "none",
    textAlign: "center" as const,
    display: "inline-block",
    padding: "12px 24px",
  },
  hr: { borderColor: "#e6ebf1", margin: "32px 0" },
  footer: { padding: "0 48px" },
  footerText: { fontSize: "12px", color: "#8898aa", lineHeight: "20px" },
  link: { color: "#0066ff" },
};

// Default props for preview
WelcomeEmail.PreviewProps = {
  userName: "Jane",
  loginUrl: "https://myapp.com/dashboard",
  guideUrl: "https://myapp.com/guide",
} satisfies WelcomeEmailProps;

export default WelcomeEmail;
```

```typescript
// lib/email.ts - Email sending service
import { Resend } from "resend";
import { WelcomeEmail } from "@/emails/welcome";
import { PasswordResetEmail } from "@/emails/password-reset";

const resend = new Resend(process.env.RESEND_API_KEY);

// Type-safe email sending
type EmailTemplate =
  | { template: "welcome"; props: { userName: string; loginUrl: string; guideUrl: string } }
  | { template: "password-reset"; props: { resetUrl: string; expiresIn: string } }
  | { template: "invoice"; props: { invoiceUrl: string; amount: string; dueDate: string } };

const templates: Record<string, React.FC<Record<string, unknown>>> = {
  welcome: WelcomeEmail,
  "password-reset": PasswordResetEmail,
};

const subjects: Record<string, (props: Record<string, unknown>) => string> = {
  welcome: () => "Welcome to MyApp!",
  "password-reset": () => "Reset your password",
  invoice: (p) => `Invoice for $${p.amount}`,
};

async function sendEmail(
  to: string,
  email: EmailTemplate
): Promise<{ id: string }> {
  const Template = templates[email.template];
  const subject = subjects[email.template](email.props);

  const { data, error } = await resend.emails.send({
    from: "MyApp <[email protected]>",
    to,
    subject,
    react: Template(email.props),
  });

  if (error) {
    throw new EmailSendError(error.message, { to, template: email.template });
  }

  return { id: data!.id };
}

export { sendEmail };
```

**Why:** React Email provides component-based email templates with TypeScript safety, hot reloading during development, and automatic conversion to email-safe HTML. Resend provides high deliverability, simple API, and React Email integration out of the box. Type-safe template definitions prevent sending emails with missing properties.

---

### Pattern 2: Email Queue with Retry Logic

**When to use:** Any production email sending. Never send email synchronously in a request handler.

**Implementation:**

```typescript
// jobs/email.ts - Background email processing
import { Queue, Worker } from "bullmq";
import { Redis } from "ioredis";
import { sendEmail } from "@/lib/email";

const connection = new Redis(process.env.REDIS_URL!, { maxRetriesPerRequest: null });

// Define the email queue
const emailQueue = new Queue("email", {
  connection,
  defaultJobOptions: {
    attempts: 3,
    backoff: {
      type: "exponential",
      delay: 60_000, // 1 min, then 2 min, then 4 min
    },

Files: 1

Size: 17.1 KB

Complexity: 21/100

Category: Web Dev

Source: https://github.com/travisjneuman/.claude/tree/main/skills/email-systems

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