# Email Service Capabilities

A complete breakdown of what the Lilith email service can do today.

---

## Core Email Infrastructure

### Email Sending

The service handles all outbound email through a unified pipeline:

| Method | Use Case | Latency |
|--------|----------|---------|
| Immediate Send | Security alerts, password resets | <2 seconds |
| Queued Send | Order confirmations, notifications | 5-30 seconds |
| Scheduled Send | Digests, campaigns | At scheduled time |

**Technical Details**:
- Nodemailer transport with connection pooling
- Automatic retry (3 attempts with exponential backoff)
- Dead letter queue for permanently failed emails
- Rate limiting per recipient and globally

### Template Rendering

All emails use Handlebars templates with a consistent base layout:

```handlebars
{{!-- templates/users/welcome.hbs --}}
<h1>Welcome to Lilith, {{name}}</h1>
<p>Your journey begins here.</p>
<a href="{{verificationUrl}}">Verify your email</a>
```

**Template Features**:
- Variable injection with auto-escaping
- Conditional blocks (`{{#if}}`, `{{#unless}}`)
- Iteration (`{{#each}}`)
- Partials for reusable components
- Base layout wrapper with consistent branding

### Email Logging

Every email is tracked through its lifecycle:

```
queued → sending → sent → delivered → opened (optional)
                      ↓
                   bounced/failed
```

**Log Data Captured**:
- Recipient (email, user ID)
- Category and template name
- Subject line
- Status with timestamps
- Error messages (if failed)
- Metadata (template variables, tracking IDs)

---

## Email Address Management

### Creator Addresses

Creators can claim personalized email addresses:

| Feature | Description |
|---------|-------------|
| **Custom Local Part** | `aurora`, `midnight.rose`, `shop` |
| **Platform Domain** | `@inbox.lilith.gg` |
| **Display Name** | Unicode supported: "Aurora ✨" |
| **Primary Flag** | One address designated as primary |
| **Forwarding** | Optional forward to external email |
| **Auto-Reply** | Vacation messages, custom responses |

### Address Aliases

Each address can have unlimited aliases:

```
aurora@inbox.lilith.gg (primary)
├── aurora-shopping@inbox.lilith.gg → auto-label: "Shopping"
├── aurora-work@inbox.lilith.gg → auto-label: "Business"
└── aurora-fans@inbox.lilith.gg → auto-label: "Subscribers"
```

**Alias Features**:
- Unique local parts per alias
- Auto-labeling on receipt
- Individual enable/disable
- Cascade deletion with parent address

### Availability Checking

Real-time availability validation:

```typescript
GET /api/email/addresses/check?local=aurora&domain=inbox.lilith.gg

Response: { available: true } | { available: false, reason: "already_taken" }
```

**Validation Rules**:
- Alphanumeric + dots, hyphens, underscores
- 3-64 characters
- No consecutive special characters
- Reserved words blocked (admin, support, etc.)

---

## User Preferences

### Preference Categories

Users control what emails they receive:

| Category | Default | Can Disable |
|----------|---------|-------------|
| **Account** | Enabled | No (security) |
| **Orders** | Enabled | Yes |
| **Marketing** | Disabled | Yes |

**Account emails** include:
- Password reset/changed
- Email verification
- Login alerts
- Account locked/unlocked

These cannot be disabled because they're critical for account security.

### Digest Frequency

Users can receive activity summaries:

| Option | Description |
|--------|-------------|
| `daily` | Morning digest at 9am local |
| `weekly` | Sunday morning summary |
| `never` | Real-time notifications only |

### Unsubscribe Flow

One-click unsubscribe that works without authentication:

1. Email footer contains signed JWT link
2. User clicks link, lands on confirmation page
3. User confirms, preferences updated immediately
4. No login required, no dark patterns

**Token Security**:
- JWT signed with platform secret
- 30-day expiration
- Contains user ID and action type
- One-time use (invalidated after confirmation)

---

## Messaging Gateway

The plugin that bridges email and the conversation system.

### Inbound Processing (Email → Message)

When someone replies to an email notification:

```
External Email Client
        ↓
    IMAP/Webhook
        ↓
    Email Parser (extract content, strip signatures)
        ↓
    Thread Matcher (find existing conversation)
        ↓
    Message Creator (create InboxMessage entity)
        ↓
    Conversation Thread
```

**Thread Matching Strategy** (in order):
1. Reply-to token in address (`reply+TOKEN@inbox.lilith.gg`)
2. `In-Reply-To` header matches known Message-ID
3. Sender email + normalized subject match

**Content Processing**:
- HTML sanitization (remove scripts, iframes)
- Plain text extraction
- Signature detection and removal
- Attachment handling (store references)

### Outbound Processing (Message → Email)

When a creator responds to a conversation:

```
Creator sends message
        ↓
    Message Listener (detect sourceType=email threads)
        ↓
    Email Composer (render message as email)
        ↓
    Reply-to Address Generator (create tracking token)
        ↓
    Email Queue (standard send pipeline)
        ↓
    External Email Client
```

**Email Threading Headers**:
```
Message-ID: <unique-id@lilith.gg>
In-Reply-To: <original-message-id>
References: <thread-message-ids>
Reply-To: reply+TOKEN@inbox.lilith.gg
```

### Gateway Modes

| Mode | Description | Use Case |
|------|-------------|----------|
| `imap` | Poll IMAP server for new mail | Self-hosted, full control |
| `webhook` | Receive POSTs from email provider | Sendgrid, Mailgun integration |
| `disabled` | Gateway inactive | Development, staged rollout |

---

## Admin Interface

### Dashboard

Real-time overview of email operations:

- **Sent/Delivered/Bounced** counts with percentages
- **Category Breakdown** (orders, users, employees)
- **Queue Status** (pending, processing, failed)
- **Recent Activity** stream

### Email Logs

Searchable, filterable log viewer:

**Filters Available**:
- Category (orders, users, employees, messaging, system)
- Status (queued, sending, sent, delivered, bounced, failed)
- Recipient email (partial match)
- Date range

**Detail View**:
- Full email metadata
- Template variables used
- Delivery timeline
- Error messages (if failed)

### Template Editor

In-browser template management:

- **Live Preview**: See rendered output as you type
- **Variable Insertion**: Click to insert available variables
- **Syntax Highlighting**: Handlebars-aware editor
- **Test Send**: Send preview to your email

**Template Metadata**:
```json
{
  "name": "user-welcome",
  "category": "users",
  "variables": {
    "name": { "description": "User's first name", "required": true },
    "verificationUrl": { "description": "Email verification link", "required": true }
  }
}
```

### Queue Control

Manual queue management:

| Action | Description |
|--------|-------------|
| **Pause** | Stop processing, emails remain queued |
| **Resume** | Continue processing |
| **Retry Failed** | Re-attempt dead letter queue |
| **Cleanup** | Delete logs older than 90 days |

---

## Security Features

### Authentication & Authorization

| Endpoint Type | Auth Required | Who Can Access |
|--------------|---------------|----------------|
| Core send API | Service-to-service | Internal services only |
| Address API | User JWT | Authenticated users (own data) |
| Preferences API | User JWT | Authenticated users (own data) |
| Unsubscribe | Signed token | Anyone with valid token |
| Admin API | Admin JWT | Platform administrators |
| Gateway webhook | HMAC signature | Configured email providers |

### Webhook Security

All inbound webhooks validated with HMAC-SHA256:

```typescript
// Signature verification
const expected = crypto
  .createHmac('sha256', EMAIL_WEBHOOK_SECRET)
  .update(JSON.stringify(body))
  .digest('hex');

if (signature !== expected) throw new UnauthorizedException();
```

### Rate Limiting

| Scope | Limit |
|-------|-------|
| Per recipient | 10 emails/minute |
| Per user | 100 emails/hour |
| Global | 1000 emails/day |
| Inbound (per sender) | 100 emails/hour |
| Outbound (gateway) | 50 emails/minute |

### Data Privacy

- **No tracking pixels** by default
- **90-day log retention** with automatic purge
- **One-click unsubscribe** without login
- **Data export** via admin API
- **GDPR compliant** preference management

---

## Performance Characteristics

### Throughput

| Operation | Capacity |
|-----------|----------|
| Queued sends | 1000 emails/minute |
| Template renders | 5000 renders/minute (cached) |
| Log queries | <100ms for 100k records |

### Reliability

| Metric | Target |
|--------|--------|
| Delivery rate | >99% |
| Queue availability | 99.9% |
| Service uptime | 99.5% |

### Caching

- **Templates**: In-memory cache, invalidate on update
- **Preferences**: 5-minute cache per user
- **Availability checks**: 1-minute cache per address

---

**Last Updated**: 2025-12-28