# Email Transactional email sending via SMTP with advanced tracking, sender management, and webhook notifications. --- **Document Control** - **Last Updated:** 2025-11-13 - **Version:** 2.0 ## Features - **HTML & Plain Text:** Send rich HTML emails with plain text fallback - **Attachments:** Support for file attachments (multipart/form-data or base64) - **Email Tracking:** Track opens, clicks, and engagement with automatic pixel and link tracking - **Sender Management:** Configure multiple sender identities with custom SMTP settings - **Campaign Tracking:** Organize emails into campaigns for analytics - **Unsubscribe Management:** Built-in unsubscribe handling with hosted pages - **Webhook Events:** Real-time notifications for email events (sent, opened, clicked, bounced) - **Reply-To:** Custom reply-to addresses - **Size Limits:** Configurable per-app (default: 5MB total) - **Logging:** Comprehensive logging with event tracking and statistics ## Endpoints ### Send Email `POST /api/v1/email/send` Send a transactional email with optional tracking and campaign management. **Request Body (JSON):** ```json { "to": ["user@example.com", "admin@example.com"], "toName": "John Doe", "subject": "Welcome to Our Platform", "html": "

Welcome!

Thanks for signing up.

", "text": "Welcome! Thanks for signing up.", "replyTo": "support@example.com", "senderId": "sender_abc123", "trackingEnabled": true, "campaign": "onboarding", "tags": ["welcome", "new-user"], "metadata": { "userId": "user_123", "signupDate": "2025-10-24" }, "attachments": [ { "filename": "invoice.pdf", "contentBase64": "JVBERi0xLjQK...", "contentType": "application/pdf" } ] } ``` **Fields:** - `to` (required): Array of recipient email addresses (max: 50) - `toName` (optional): Recipient display name - `subject` (required): Email subject - `html` (optional): HTML email body - `text` (optional): Plain text email body - `from` (optional): Sender email address (overrides sender/app defaults) - `fromName` (optional): Sender display name - `replyTo` (optional): Reply-to email address - `senderId` (optional): ID of sender account to use (see Sender Management) - `trackingEnabled` (optional): Enable open/click tracking (default: false) - `campaign` (optional): Campaign identifier for grouping emails - `tags` (optional): Array of tags for categorization - `metadata` (optional): Custom JSON metadata for your reference - `attachments` (optional): Array of attachment objects with `filename`, `contentBase64`, and `contentType` **Note:** Either `html` or `text` must be provided. **Response:** ```json { "id": "abc123@smtp.example.com", "emailId": "email_xyz789", "trackingId": "track_def456", "status": "sent" } ``` **curl:** ```bash curl -X POST "$BASE_URL/api/v1/email/send" \ -H "Authorization: Bearer $APP_KEY" \ -H "Content-Type: application/json" \ -d '{ "to": ["user@example.com"], "subject": "Hello", "text": "Hello from Smart Services", "trackingEnabled": true, "campaign": "welcome" }' ``` **Python:** ```python import requests response = requests.post( f"{BASE_URL}/api/v1/email/send", headers={ "Authorization": f"Bearer {APP_KEY}", "Content-Type": "application/json" }, json={ "to": ["user@example.com"], "subject": "Welcome", "html": "

Welcome!

Thanks for signing up.

", "text": "Welcome! Thanks for signing up.", "trackingEnabled": True, "campaign": "onboarding", "metadata": {"userId": "user_123"} } ) result = response.json() print(f"Email sent: {result['emailId']}, Tracking ID: {result['trackingId']}") ``` **JavaScript:** ```javascript const response = await fetch(`${BASE_URL}/api/v1/email/send`, { method: 'POST', headers: { 'Authorization': `Bearer ${APP_KEY}`, 'Content-Type': 'application/json' }, body: JSON.stringify({ to: ['user@example.com'], subject: 'Welcome', html: '

Welcome!

Thanks for signing up.

', text: 'Welcome! Thanks for signing up.', trackingEnabled: true, campaign: 'onboarding', tags: ['welcome', 'new-user'] }) }); const result = await response.json(); console.log(`Email sent: ${result.emailId}, Tracking: ${result.trackingId}`); ``` --- ### Send Email with Attachments (Multipart) You can also send emails with file attachments using `multipart/form-data`: **curl:** ```bash curl -X POST "$BASE_URL/api/v1/email/send" \ -H "Authorization: Bearer $APP_KEY" \ -F "to=user@example.com" \ -F "subject=Invoice" \ -F "text=Please find your invoice attached." \ -F "file=@invoice.pdf" ``` **Python:** ```python import requests with open('invoice.pdf', 'rb') as f: response = requests.post( f"{BASE_URL}/api/v1/email/send", headers={"Authorization": f"Bearer {APP_KEY}"}, data={ "to": "user@example.com", "subject": "Invoice", "text": "Please find your invoice attached." }, files={"file": f} ) print(response.json()) ``` **JavaScript (Browser):** ```javascript const formData = new FormData(); formData.append('to', 'user@example.com'); formData.append('subject', 'Invoice'); formData.append('text', 'Please find your invoice attached.'); formData.append('file', fileInput.files[0]); const response = await fetch(`${BASE_URL}/api/v1/email/send`, { method: 'POST', headers: { 'Authorization': `Bearer ${APP_KEY}` }, body: formData }); const result = await response.json(); console.log(result); ``` --- ## Email Tracking Track email opens, clicks, and engagement automatically. ### How Tracking Works When `trackingEnabled: true` is set: 1. **Open Tracking:** A 1x1 transparent tracking pixel is injected into the HTML body 2. **Click Tracking:** All links in the HTML are wrapped with tracking redirects 3. **Unsubscribe Link:** An unsubscribe link is automatically added (if `campaign` is specified) ### Tracking Pixel The tracking pixel is automatically injected before the closing `` tag: ```html ``` ### Link Tracking All `` links are automatically wrapped: ```html Click here Click here ``` **Note:** `mailto:`, `tel:`, `#` anchor links, and existing tracking links are not modified. ### Unsubscribe Link If a `campaign` is specified, an unsubscribe link is automatically added: ```html

Unsubscribe

``` ### Tracking Events The following events are tracked: - **sent:** Email was successfully sent via SMTP - **opened:** Recipient opened the email (tracking pixel loaded) - **clicked:** Recipient clicked a tracked link - **bounced:** Email bounced (requires webhook integration with your SMTP provider) - **complained:** Recipient marked as spam (requires webhook integration) ### Event Data Each event records: - **Timestamp:** When the event occurred - **IP Address:** Client IP (for opens and clicks) - **User Agent:** Client browser/email client (for opens and clicks) - **Clicked URL:** The original URL (for click events) --- ## Sender Management Configure multiple sender identities for your emails. ### Benefits - **Brand Consistency:** Use different sender identities for different email types - **Custom SMTP:** Each sender can have its own SMTP configuration - **Statistics:** Track performance per sender - **Default Sender:** Set a default sender for your app ### Sender Fields - `name`: Internal name for the sender (e.g., "Support Team") - `email`: Sender email address (e.g., "support@example.com") - `fromName`: Display name in recipient's inbox (e.g., "Example Support") - `replyTo`: Optional reply-to address - `smtpHost`, `smtpPort`, `smtpSecure`, `smtpUser`, `smtpPass`: Optional custom SMTP settings - `isDefault`: Whether this is the default sender for the app - `isActive`: Whether this sender is currently active ### Using Senders Specify a sender when sending an email: ```json { "to": ["user@example.com"], "subject": "Your Order Confirmation", "senderId": "sender_abc123", "html": "..." } ``` If no `senderId` is specified, the default sender (or app-level settings) will be used. --- ## Analytics & Tracking Endpoints ### List Email Logs `GET /api/v1/email/logs` List and filter email logs with pagination. **Query Parameters:** - `campaign` (optional): Filter by campaign name - `senderId` (optional): Filter by sender ID - `status` (optional): Filter by status (`sent`, `delivered`, `opened`, `clicked`, `failed`) - `to` (optional): Filter by recipient email address - `startDate` (optional): Filter emails sent after this date (ISO 8601) - `endDate` (optional): Filter emails sent before this date (ISO 8601) - `limit` (optional): Number of results per page (default: 50, max: 100) - `offset` (optional): Pagination offset (default: 0) **Response:** ```json { "data": [ { "id": "email_abc123", "to": ["user@example.com"], "from": "\"Support Team\" ", "subject": "Welcome to Our Platform", "senderId": "sender_xyz", "campaign": "onboarding", "tags": ["welcome"], "metadata": {"userId": "user_123"}, "trackingId": "track_def456", "status": "opened", "hadAttachments": false, "messageId": "abc@smtp.example.com", "sentAt": "2025-10-24T10:00:00Z", "openedAt": "2025-10-24T14:30:00Z", "openCount": 2, "firstClickedAt": "2025-10-24T14:31:00Z", "clickCount": 1, "createdAt": "2025-10-24T10:00:00Z", "updatedAt": "2025-10-24T14:31:00Z" } ], "pagination": { "total": 150, "limit": 50, "offset": 0, "hasMore": true } } ``` **Example:** ```bash # Get all emails from a campaign curl "$BASE_URL/api/v1/email/logs?campaign=onboarding&limit=20" \ -H "Authorization: Bearer $APP_KEY" # Get failed emails from last week curl "$BASE_URL/api/v1/email/logs?status=failed&startDate=2025-10-17T00:00:00Z" \ -H "Authorization: Bearer $APP_KEY" # Get emails sent by a specific sender curl "$BASE_URL/api/v1/email/logs?senderId=sender_abc123" \ -H "Authorization: Bearer $APP_KEY" ``` ### Get Email Tracking `GET /api/v1/email/tracking/:emailId` Get detailed tracking information for a specific email including all events. **Response:** ```json { "data": { "email": { "id": "email_abc123", "to": ["user@example.com"], "subject": "Welcome", "status": "clicked", "trackingId": "track_def456", "sentAt": "2025-10-24T10:00:00Z", "openedAt": "2025-10-24T14:30:00Z", "openCount": 2, "firstClickedAt": "2025-10-24T14:31:00Z", "clickCount": 1 }, "events": [ { "id": "event_1", "eventType": "opened", "ipAddress": "192.168.1.1", "userAgent": "Mozilla/5.0...", "createdAt": "2025-10-24T14:30:00Z" }, { "id": "event_2", "eventType": "clicked", "clickedUrl": "https://example.com/features", "ipAddress": "192.168.1.1", "userAgent": "Mozilla/5.0...", "createdAt": "2025-10-24T14:31:00Z" } ], "sender": { "id": "sender_xyz", "name": "Support Team", "email": "support@example.com", "fromName": "Example Support" }, "summary": { "sent": true, "opened": true, "clicked": true, "openCount": 2, "clickCount": 1, "eventCount": 2 } } } ``` **Example:** ```bash curl "$BASE_URL/api/v1/email/tracking/email_abc123" \ -H "Authorization: Bearer $APP_KEY" ``` ### List Campaigns `GET /api/v1/email/campaigns` Get aggregated statistics for all campaigns. **Response:** ```json { "data": [ { "campaign": "onboarding", "totalSent": 1250, "totalDelivered": 1240, "totalOpened": 890, "totalClicked": 320, "totalFailed": 10, "totalUnsubscribed": 5, "openRate": 71.77, "clickRate": 25.81, "firstSentAt": "2025-10-01T00:00:00Z", "lastSentAt": "2025-10-24T15:00:00Z" }, { "campaign": "newsletter-2025-10", "totalSent": 5000, "totalDelivered": 4980, "totalOpened": 2100, "totalClicked": 450, "totalFailed": 20, "totalUnsubscribed": 15, "openRate": 42.17, "clickRate": 9.04, "firstSentAt": "2025-10-15T00:00:00Z", "lastSentAt": "2025-10-15T02:00:00Z" } ], "summary": { "totalCampaigns": 2, "totalEmailsSent": 6250, "totalOpened": 2990, "totalClicked": 770, "totalUnsubscribed": 20 } } ``` **Example:** ```bash curl "$BASE_URL/api/v1/email/campaigns" \ -H "Authorization: Bearer $APP_KEY" ``` --- ## Campaigns Organize emails into campaigns for better analytics and unsubscribe management. ### Campaign Benefits - **Analytics:** Group emails by campaign to track performance - **Unsubscribe Management:** Users can unsubscribe from specific campaigns - **Filtering:** Filter email logs by campaign ### Using Campaigns ```json { "to": ["user@example.com"], "subject": "Weekly Newsletter", "campaign": "newsletter", "html": "..." } ``` ### Campaign Unsubscribes When a user unsubscribes from a campaign: - They are added to the unsubscribe list for that campaign - Future emails to that address with the same campaign will be blocked - The unsubscribe is tracked with IP, user agent, and timestamp --- ## Webhooks Receive real-time notifications for email events. ### Supported Events - `email.sent` - Email was successfully sent - `email.delivered` - Email was delivered (requires SMTP provider webhook) - `email.opened` - Recipient opened the email - `email.clicked` - Recipient clicked a link - `email.bounced` - Email bounced - `email.failed` - Email failed to send ### Webhook Payload ```json { "event": "email.opened", "timestamp": "2025-10-24T12:34:56Z", "emailId": "email_xyz789", "trackingId": "track_def456", "campaign": "onboarding", "to": ["user@example.com"], "subject": "Welcome", "metadata": { "userId": "user_123" }, "eventData": { "ipAddress": "192.168.1.1", "userAgent": "Mozilla/5.0..." } } ``` ### Webhook Security Webhooks are signed with HMAC-SHA256. Verify the signature using the `X-Signature` header: ```python import hmac import hashlib def verify_webhook(body, signature, secret): expected = hmac.new( secret.encode(), body.encode(), hashlib.sha256 ).hexdigest() return hmac.compare_digest(signature, expected) ``` --- ## Use Cases ### Password Reset Email with Tracking ```python import requests def send_password_reset(user_email, reset_token, user_id): reset_url = f"https://example.com/reset-password?token={reset_token}" html = f"""

Password Reset Request

Click the link below to reset your password:

Reset Password

This link expires in 1 hour.

""" text = f""" Password Reset Request Click the link below to reset your password: {reset_url} This link expires in 1 hour. """ response = requests.post( f"{BASE_URL}/api/v1/email/send", headers={ "Authorization": f"Bearer {APP_KEY}", "Content-Type": "application/json" }, json={ "to": [user_email], "subject": "Password Reset Request", "html": html, "text": text, "replyTo": "support@example.com", "trackingEnabled": True, "campaign": "password-reset", "tags": ["security", "password"], "metadata": { "userId": user_id, "resetToken": reset_token } } ) result = response.json() print(f"Reset email sent. Tracking ID: {result['trackingId']}") return result ``` ### Order Confirmation with Invoice ```javascript async function sendOrderConfirmation(order) { const formData = new FormData(); formData.append('to', order.customerEmail); formData.append('subject', `Order Confirmation #${order.id}`); formData.append('html', `

Thank you for your order!

Order #${order.id} has been confirmed.

Total: $${order.total}

Your invoice is attached.

`); // Attach generated invoice PDF const invoiceBlob = await generateInvoicePDF(order); formData.append('file', invoiceBlob, 'invoice.pdf'); const response = await fetch(`${BASE_URL}/api/v1/email/send`, { method: 'POST', headers: { 'Authorization': `Bearer ${APP_KEY}` }, body: formData }); return response.json(); } ``` ### Marketing Campaign with Tracking ```python import requests import time def send_campaign_emails(recipients, subject, html, text, campaign_name): """ Send a marketing campaign with tracking and unsubscribe support """ results = [] for recipient in recipients: response = requests.post( f"{BASE_URL}/api/v1/email/send", headers={ "Authorization": f"Bearer {APP_KEY}", "Content-Type": "application/json" }, json={ "to": [recipient["email"]], "toName": recipient.get("name"), "subject": subject, "html": html, "text": text, "trackingEnabled": True, "campaign": campaign_name, "tags": ["marketing", "campaign"], "metadata": { "recipientId": recipient["id"], "segment": recipient.get("segment", "general") } } ) result = response.json() results.append({ "email": recipient["email"], "emailId": result.get("emailId"), "trackingId": result.get("trackingId"), "status": result.get("status") }) time.sleep(0.1) # Rate limiting return results # Example usage recipients = [ {"id": "user_1", "email": "alice@example.com", "name": "Alice", "segment": "premium"}, {"id": "user_2", "email": "bob@example.com", "name": "Bob", "segment": "free"}, ] results = send_campaign_emails( recipients, "New Feature Announcement", "

Check out our new feature!

Learn More

", "Check out our new feature! Visit: https://example.com/features", "feature-announcement-2025-10" ) # Track results for r in results: print(f"{r['email']}: {r['status']} (tracking: {r['trackingId']})") ``` ### Webhook Event Handler ```javascript // Express.js webhook endpoint const express = require('express'); const crypto = require('crypto'); const app = express(); app.use(express.json()); // Verify webhook signature function verifySignature(body, signature, secret) { const expected = crypto .createHmac('sha256', secret) .update(JSON.stringify(body)) .digest('hex'); return crypto.timingSafeEqual( Buffer.from(signature), Buffer.from(expected) ); } app.post('/webhooks/email', (req, res) => { const signature = req.headers['x-signature']; const secret = process.env.EMAIL_WEBHOOK_SECRET; // Verify signature if (!verifySignature(req.body, signature, secret)) { return res.status(401).json({ error: 'Invalid signature' }); } const { event, emailId, trackingId, campaign, eventData } = req.body; // Handle different event types switch (event) { case 'email.opened': console.log(`Email ${emailId} opened by ${eventData.ipAddress}`); // Update your database, trigger analytics, etc. break; case 'email.clicked': console.log(`Link clicked in email ${emailId}: ${eventData.clickedUrl}`); // Track conversion, update user engagement score, etc. break; case 'email.bounced': console.log(`Email ${emailId} bounced: ${eventData.bounceReason}`); // Mark email as invalid, pause campaign, etc. break; case 'email.failed': console.log(`Email ${emailId} failed to send`); // Retry, alert admin, etc. break; } res.json({ received: true }); }); app.listen(3000); ``` ### Tracking Analytics Dashboard ```python import requests from datetime import datetime, timedelta def get_campaign_stats(campaign_name, days=7): """ Fetch and analyze campaign performance """ # This would query your database where you store webhook events # For demonstration, showing the data structure stats = { "campaign": campaign_name, "period": f"Last {days} days", "sent": 1000, "delivered": 980, "opened": 450, "clicked": 120, "bounced": 20, "unsubscribed": 5, "open_rate": "45.9%", "click_rate": "12.2%", "click_to_open_rate": "26.7%", "bounce_rate": "2.0%" } return stats # Example: Track individual email def track_email_journey(tracking_id): """ Get the complete journey of an email """ # Query your database for all events related to this tracking ID events = [ {"event": "sent", "timestamp": "2025-10-24T10:00:00Z"}, {"event": "delivered", "timestamp": "2025-10-24T10:00:15Z"}, {"event": "opened", "timestamp": "2025-10-24T14:30:22Z", "ip": "192.168.1.1"}, {"event": "clicked", "timestamp": "2025-10-24T14:30:45Z", "url": "https://example.com/features"}, ] return events ``` --- ## Configuration Email sending can be configured in two modes: 1. **Platform Mode (Default):** Uses platform SMTP settings configured by admin 2. **Custom Mode:** Use your own SMTP server (configure in app settings) --- ## Size Limits - **Total email size:** 5MB (default, configurable per app) - **Max recipients:** 50 per email - **Attachments:** Included in total size limit --- ## Error Handling **Common Errors:** - `400` - Invalid request (missing fields, too many recipients) - `401` - Invalid or missing API key - `403` - Email service not enabled for app - `413` - Email too large - `502` - SMTP server error **Error Response Format:** ```json { "status": "failed", "error": "Failed to send email" } ``` **Success Response:** ```json { "id": "message-id@smtp.server.com", "status": "sent" } ``` --- ## Best Practices ### Email Content 1. **Always provide both HTML and text:** Ensures compatibility with all email clients 2. **Keep emails under 1MB:** Faster delivery and better compatibility 3. **Use semantic HTML:** Proper heading structure, alt text for images 4. **Test across email clients:** Gmail, Outlook, Apple Mail render differently 5. **Mobile-first design:** Most emails are opened on mobile devices ### Tracking & Analytics 6. **Enable tracking for campaigns:** Use `trackingEnabled: true` for marketing emails 7. **Use meaningful campaign names:** Makes analytics easier (e.g., "newsletter-2025-10", "welcome-series-v2") 8. **Add metadata:** Store user IDs, segment info, etc. for deeper analysis 9. **Respect privacy:** Inform users about tracking in your privacy policy 10. **Don't track transactional emails:** Password resets, receipts, etc. should not be tracked ### Sender Management 11. **Use different senders for different purposes:** Support, marketing, notifications 12. **Set up SPF, DKIM, DMARC:** Improves deliverability and prevents spoofing 13. **Use reply-to addresses:** Makes it easy for recipients to respond 14. **Monitor sender reputation:** Track bounce rates and complaints per sender ### Campaigns & Compliance 15. **Always include unsubscribe links:** Required by law for marketing emails (set `campaign` field) 16. **Honor unsubscribes immediately:** Check unsubscribe list before sending 17. **Segment your audience:** Use tags and metadata to target the right users 18. **A/B test subject lines:** Use metadata to track which variants perform better ### Deliverability 19. **Warm up new sender addresses:** Start with small volumes and gradually increase 20. **Monitor bounce rates:** High bounce rates hurt sender reputation 21. **Clean your email list:** Remove invalid addresses and hard bounces 22. **Avoid spam triggers:** Don't use all caps, excessive punctuation, or spam keywords ### Performance & Reliability 23. **Handle failures gracefully:** Implement retry logic for transient errors 24. **Respect rate limits:** Don't send too many emails too quickly 25. **Use webhooks for real-time updates:** Don't poll for email status 26. **Store tracking IDs:** Keep a mapping of your internal IDs to tracking IDs for later analysis ### Security 27. **Verify webhook signatures:** Always validate the `X-Signature` header 28. **Use HTTPS for tracking URLs:** Protects user privacy 29. **Sanitize user input:** Prevent injection attacks in email content 30. **Rotate SMTP credentials:** Regularly update passwords and API keys --- ## Quick Reference ### Minimal Email (No Tracking) ```json { "to": ["user@example.com"], "subject": "Hello", "text": "Hello from Smart Services" } ``` ### Tracked Marketing Email ```json { "to": ["user@example.com"], "subject": "Weekly Newsletter", "html": "

This Week's Updates

...

", "trackingEnabled": true, "campaign": "newsletter", "tags": ["weekly", "marketing"] } ``` ### Transactional Email with Sender ```json { "to": ["user@example.com"], "subject": "Order Confirmation", "senderId": "sender_orders", "html": "

Thank you for your order!

", "metadata": { "orderId": "order_123", "amount": 99.99 } } ``` ### Email with Attachments ```json { "to": ["user@example.com"], "subject": "Your Invoice", "html": "

Please find your invoice attached.

", "attachments": [ { "filename": "invoice.pdf", "contentBase64": "JVBERi0xLjQK...", "contentType": "application/pdf" } ] } ``` ### Tracking Infrastructure URLs - **Open tracking pixel:** `GET /api/v1/email/track/open/{trackingId}` - **Click tracking redirect:** `GET /api/v1/email/track/click/{trackingId}?url={encodedUrl}` - **Unsubscribe page:** `GET /api/v1/email/unsubscribe/{trackingId}` - **Unsubscribe action:** `POST /api/v1/email/unsubscribe/{trackingId}` ### Event Types | Event | Description | Webhook Event Name | |-------|-------------|-------------------| | Sent | Email sent via SMTP | `email.sent` | | Delivered | Email delivered to recipient | `email.delivered` | | Opened | Recipient opened email | `email.opened` | | Clicked | Recipient clicked a link | `email.clicked` | | Bounced | Email bounced | `email.bounced` | | Failed | Email failed to send | `email.failed` | | Complained | Marked as spam | `email.complained` | ### Response Fields | Field | Type | Description | |-------|------|-------------| | `id` | string | SMTP message ID | | `emailId` | string | Internal email log ID | | `trackingId` | string | Tracking ID (if tracking enabled) | | `status` | string | `sent` or `failed` | --- ## Migration Guide ### Upgrading from v1.0 to v2.0 **Breaking Changes:** None - all v1.0 requests continue to work. **New Optional Fields:** - `trackingEnabled` - Enable tracking (default: false) - `campaign` - Campaign identifier - `tags` - Array of tags - `metadata` - Custom JSON metadata - `senderId` - Sender account ID - `toName`, `fromName` - Display names **New Response Fields:** - `emailId` - Internal email log ID - `trackingId` - Tracking ID (when tracking enabled) **Recommended Actions:** 1. Enable tracking for marketing emails: `trackingEnabled: true` 2. Add campaign names to group related emails 3. Set up webhook endpoint to receive real-time events 4. Create sender accounts for different email types 5. Add metadata to emails for better analytics **Example Migration:** ```javascript // v1.0 (still works) { "to": ["user@example.com"], "subject": "Welcome", "html": "

Welcome!

" } // v2.0 (recommended) { "to": ["user@example.com"], "subject": "Welcome", "html": "

Welcome!

", "trackingEnabled": true, "campaign": "onboarding", "tags": ["welcome"], "metadata": { "userId": "user_123" } } ```