---
name: communication-systems
description: Email, notifications, and messaging system patterns
domain: domain-applications
version: 1.0.0
tags: [email, notifications, push, webhooks, messaging]
triggers:
  keywords:
    primary: [email, notification, push notification, webhook, messaging]
    secondary: [transactional email, fcm, web push, in-app notification, resend]
  context_boost: [send, alert, notify, communicate]
  context_penalty: [game, frontend, ui]
  priority: medium
---

# Communication Systems

## Overview

Building email systems, push notifications, in-app messaging, and webhook integrations.

---

## Email Systems

### Transactional Email

```typescript
import { Resend } from 'resend';

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

interface EmailOptions {
  to: string | string[];
  subject: string;
  html?: string;
  text?: string;
  template?: string;
  data?: Record<string, any>;
  attachments?: Array<{
    filename: string;
    content: Buffer | string;
  }>;
}

async function sendEmail(options: EmailOptions) {
  let html = options.html;

  // Use template if specified
  if (options.template) {
    html = await renderTemplate(options.template, options.data);
  }

  const { data, error } = await resend.emails.send({
    from: 'noreply@example.com',
    to: options.to,
    subject: options.subject,
    html,
    text: options.text,
    attachments: options.attachments,
  });

  if (error) {
    console.error('Email send failed:', error);
    throw error;
  }

  // Log for tracking
  await prisma.emailLog.create({
    data: {
      messageId: data.id,
      to: Array.isArray(options.to) ? options.to.join(',') : options.to,
      subject: options.subject,
      template: options.template,
      status: 'sent',
    },
  });

  return data;
}

// Email templates with React Email
import { render } from '@react-email/render';
import { WelcomeEmail } from './templates/WelcomeEmail';
import { PasswordResetEmail } from './templates/PasswordResetEmail';

const templates = {
  welcome: WelcomeEmail,
  passwordReset: PasswordResetEmail,
};

async function renderTemplate(name: string, data: Record<string, any>) {
  const Template = templates[name];
  if (!Template) throw new Error(`Template ${name} not found`);

  return render(<Template {...data} />);
}

// React Email template
import {
  Html, Head, Body, Container, Text, Button, Img,
} from '@react-email/components';

function WelcomeEmail({ name, actionUrl }: { name: string; actionUrl: string }) {
  return (
    <Html>
      <Head />
      <Body style={{ fontFamily: 'Arial, sans-serif' }}>
        <Container>
          <Img src="https://example.com/logo.png" width="120" height="40" alt="Logo" />
          <Text>Hi {name},</Text>
          <Text>Welcome to our platform! Get started by setting up your account.</Text>
          <Button
            href={actionUrl}
            style={{ background: '#007bff', color: '#fff', padding: '12px 24px' }}
          >
            Get Started
          </Button>
        </Container>
      </Body>
    </Html>
  );
}
```

### Email Queue

```typescript
import Bull from 'bull';

const emailQueue = new Bull('email', process.env.REDIS_URL);

// Add to queue
async function queueEmail(options: EmailOptions, delay?: number) {
  return emailQueue.add('send', options, {
    delay,
    attempts: 3,
    backoff: { type: 'exponential', delay: 60000 },
  });
}

// Process queue
emailQueue.process('send', async (job) => {
  await sendEmail(job.data);
});

// Handle failures
emailQueue.on('failed', async (job, error) => {
  console.error(`Email job ${job.id} failed:`, error);

  await prisma.emailLog.update({
    where: { jobId: job.id },
    data: { status: 'failed', error: error.message },
  });
});

// Bulk email with rate limiting
async function sendBulkEmail(recipients: string[], template: string, data: Record<string, any>) {
  const jobs = recipients.map((to, index) => ({
    name: 'send',
    data: { to, template, data },
    opts: { delay: index * 100 }, // Stagger sends
  }));

  await emailQueue.addBulk(jobs);
}
```

---

## Push Notifications

### Web Push

```typescript
import webpush from 'web-push';

webpush.setVapidDetails(
  'mailto:admin@example.com',
  process.env.VAPID_PUBLIC_KEY!,
  process.env.VAPID_PRIVATE_KEY!
);

interface PushSubscription {
  endpoint: string;
  keys: {
    p256dh: string;
    auth: string;
  };
}

// Store subscription
async function saveSubscription(userId: string, subscription: PushSubscription) {
  await prisma.pushSubscription.upsert({
    where: { endpoint: subscription.endpoint },
    update: { keys: subscription.keys },
    create: {
      userId,
      endpoint: subscription.endpoint,
      keys: subscription.keys,
    },
  });
}

// Send push notification
async function sendPush(userId: string, payload: {
  title: string;
  body: string;
  icon?: string;
  url?: string;
  data?: Record<string, any>;
}) {
  const subscriptions = await prisma.pushSubscription.findMany({
    where: { userId },
  });

  const results = await Promise.allSettled(
    subscriptions.map(async (sub) => {
      try {
        await webpush.sendNotification(
          { endpoint: sub.endpoint, keys: sub.keys },
          JSON.stringify(payload)
        );
      } catch (error) {
        if (error.statusCode === 410) {
          // Subscription expired, remove it
          await prisma.pushSubscription.delete({ where: { id: sub.id } });
        }
        throw error;
      }
    })
  );

  return results;
}

// Service worker handler
// public/sw.js
self.addEventListener('push', (event) => {
  const data = event.data.json();

  event.waitUntil(
    self.registration.showNotification(data.title, {
      body: data.body,
      icon: data.icon || '/icon-192.png',
      data: data,
    })
  );
});

self.addEventListener('notificationclick', (event) => {
  event.notification.close();

  if (event.notification.data.url) {
    event.waitUntil(clients.openWindow(event.notification.data.url));
  }
});
```

### Mobile Push (FCM)

```typescript
import admin from 'firebase-admin';

admin.initializeApp({
  credential: admin.credential.cert(serviceAccount),
});

interface MobileNotification {
  title: string;
  body: string;
  imageUrl?: string;
  data?: Record<string, string>;
}

async function sendMobilePush(
  tokens: string[],
  notification: MobileNotification
) {
  const message: admin.messaging.MulticastMessage = {
    tokens,
    notification: {
      title: notification.title,
      body: notification.body,
      imageUrl: notification.imageUrl,
    },
    data: notification.data,
    android: {
      priority: 'high',
      notification: {
        sound: 'default',
        clickAction: 'OPEN_ACTIVITY',
      },
    },
    apns: {
      payload: {
        aps: {
          sound: 'default',
          badge: 1,
        },
      },
    },
  };

  const response = await admin.messaging().sendEachForMulticast(message);

  // Handle failures
  response.responses.forEach((resp, idx) => {
    if (!resp.success) {
      const errorCode = resp.error?.code;
      if (
        errorCode === 'messaging/invalid-registration-token' ||
        errorCode === 'messaging/registration-token-not-registered'
      ) {
        // Remove invalid token
        removeDeviceToken(tokens[idx]);
      }
    }
  });

  return response;
}
```

---

## In-App Notifications

```typescript
interface Notification {
  id: string;
  userId: string;
  type: string;
  title: string;
  message: string;
  data?: Record<string, any>;
  read: boolean;
  createdAt: Date;
}

// Create notification
async function createNotification(params: {
  userId: string;
  type: string;
  title: string;
  message: string;
  data?: Record<string, any>;
}) {
  const notification = await prisma.notification.create({
    data: {
      ...params,
      read: false,
    },
  });

  // Send real-time update
  await pubsub.publish(`notifications:${params.userId}`, {
    type: 'NEW_NOTIFICATION',
    notification,
  });

  return notification;
}

// Get notifications with pagination
async function getNotifications(userId: string, options: {
  page?: number;
  limit?: number;
  unreadOnly?: boolean;
}) {
  const { page = 1, limit = 20, unreadOnly = false } = options;

  const where = {
    userId,
    ...(unreadOnly && { read: false }),
  };

  const [notifications, total, unreadCount] = await Promise.all([
    prisma.notification.findMany({
      where,
      orderBy: { createdAt: 'desc' },
      skip: (page - 1) * limit,
      take: limit,
    }),
    prisma.notification.count({ where }),
    prisma.notification.count({ where: { userId, read: false } }),
  ]);

  return { notifications, total, unreadCount };
}

// Mark as read
async function markAsRead(userId: string, notificationIds: string[]) {
  await prisma.notification.updateMany({
    where: {
      id: { in: notificationIds },
      userId,
    },
    data: { read: true },
  });
}

// React hook for notifications
function useNotifications() {
  const [notifications, setNotifications] = useState<Notification[]>([]);
  const [unreadCount, setUnreadCount] = useState(0);

  useEffect(() => {
    // Initial fetch
    fetchNotifications().then(({ notifications, unreadCount }) => {
      setNotifications(notifications);
      setUnreadCount(unreadCount);
    });

    // Subscribe to real-time updates
    const unsubscribe = subscribeToNotifications((notification) => {
      setNotifications((prev) => [notification, ...prev]);
      setUnreadCount((prev) => prev + 1);
    });

    return unsubscribe;
  }, []);

  return { notifications, unreadCount, markAsRead };
}
```

---

## Webhooks

```typescript
interface Webhook {
  id: string;
  url: string;
  secret: string;
  events: string[];
  active: boolean;
}

// Register webhook
async function registerWebhook(params: {
  url: string;
  events: string[];
}) {
  const secret = crypto.randomBytes(32).toString('hex');

  return prisma.webhook.create({
    data: {
      url: params.url,
      events: params.events,
      secret,
      active: true,
    },
  });
}

// Send webhook
async function sendWebhook(webhookId: string, event: string, payload: any) {
  const webhook = await prisma.webhook.findUnique({ where: { id: webhookId } });
  if (!webhook || !webhook.active) return;

  const timestamp = Date.now().toString();
  const body = JSON.stringify({ event, data: payload, timestamp });

  // Create signature
  const signature = crypto
    .createHmac('sha256', webhook.secret)
    .update(body)
    .digest('hex');

  try {
    const response = await fetch(webhook.url, {
      method: 'POST',
      headers: {
        'Content-Type': 'application/json',
        'X-Webhook-Signature': signature,
        'X-Webhook-Timestamp': timestamp,
      },
      body,
    });

    await prisma.webhookLog.create({
      data: {
        webhookId,
        event,
        payload,
        responseStatus: response.status,
        success: response.ok,
      },
    });

    // Disable after multiple failures
    if (!response.ok) {
      await handleWebhookFailure(webhookId);
    }
  } catch (error) {
    await prisma.webhookLog.create({
      data: {
        webhookId,
        event,
        payload,
        error: error.message,
        success: false,
      },
    });

    await handleWebhookFailure(webhookId);
  }
}

// Verify webhook signature (receiver side)
function verifyWebhookSignature(
  body: string,
  signature: string,
  secret: string
): boolean {
  const expected = crypto
    .createHmac('sha256', secret)
    .update(body)
    .digest('hex');

  return crypto.timingSafeEqual(
    Buffer.from(signature),
    Buffer.from(expected)
  );
}
```

---

## Related Skills

- [[realtime-systems]] - Real-time messaging
- [[backend]] - API development
- [[reliability-engineering]] - Delivery guarantees



---
Source attribution: miles990
Original project: https://github.com/miles990/claude-software-skills/blob/73632f218e5b3e9d29c87b00c7955964f354833d/domain-applications/communication-systems/SKILL.md
License: MIT
License information: https://opensource.org/license/mit
Original upstream instructions; downloaded from Dave AI.

## Upstream license notice

MIT License

Copyright (c) 2025

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.



# Dave AI resource metadata

Creator / publisher: miles990
Original project: https://github.com/miles990/claude-software-skills/blob/73632f218e5b3e9d29c87b00c7955964f354833d/domain-applications/communication-systems/SKILL.md
Attribution basis: Recovered original package and original project license at a pinned revision

Fields of work: Marketing, Sales
Roles: Customer Success Manager, Email Marketer, Growth Marketer
Specialties: API
Tools: Bull, Resend, Web Push
Country applicability: Country not specified
Classification basis: Source catalog labels
Instruction SHA-256: c8d6e1070aee4f548076f67472269487d92d728c6e94fa8c01c8789e3b2c1087
Metadata reviewed: 2026-10-27
This metadata supersedes earlier Dave AI catalog attribution. Original instruction and supporting files are preserved.