Architecture Design

SirrChat adopts a modular architecture to provide a flexible and extensible email server solution.

Overall Architecture

┌─────────────────────────────────────────────┐
│           Client Layer                      │
│  (Thunderbird, Outlook, Mobile Apps)        │
└──────────────┬──────────────────────────────┘
               │
               ▼
┌─────────────────────────────────────────────┐
│           Protocol Layer                    │
│  ┌─────────┐  ┌─────────┐  ┌─────────┐    │
│  │  SMTP   │  │  IMAP   │  │Submission│    │
│  └─────────┘  └─────────┘  └─────────┘    │
└──────────────┬──────────────────────────────┘
               │
               ▼
┌─────────────────────────────────────────────┐
│           Authentication Layer              │
│  ┌──────────┐  ┌─────┐  ┌─────┐  ┌──────┐ │
│  │Blockchain│  │LDAP │  │ PAM │  │Custom│ │
│  └──────────┘  └─────┘  └─────┘  └──────┘ │
└──────────────┬──────────────────────────────┘
               │
               ▼
┌─────────────────────────────────────────────┐
│           Processing Layer                  │
│  ┌─────────┐  ┌──────┐  ┌─────────┐       │
│  │  Filter │  │Modify│  │  Check  │       │
│  │  (Sieve)│  │(DKIM)│  │(SPF/etc)│       │
│  └─────────┘  └──────┘  └─────────┘       │
└──────────────┬──────────────────────────────┘
               │
               ▼
┌─────────────────────────────────────────────┐
│           Storage Layer                     │
│  ┌──────────┐  ┌────────────┐             │
│  │ Database │  │  Storage   │             │
│  │(PG/MySQL)│  │(Local/S3)  │             │
│  └──────────┘  └────────────┘             │
└─────────────────────────────────────────────┘

Core Components

Protocol Handlers

SMTP Server

• Receive and send emails
• Support STARTTLS encryption
• Implement rate limiting and anti-spam measures

IMAP Server

• Email storage and retrieval
• Folder management
• Email search functionality
• Support IDLE push notifications

Submission Server

• Email submission (port 587)
• Mandatory authentication
• Automatic DKIM signing

Authentication Module

Blockchain Authentication

type BlockchainAuth struct {
    networks map[string]RPCClient
    cache    *AuthCache
}

func (b *BlockchainAuth) Verify(address, signature, message string) bool {
    // 1. Recover signer address
    // 2. Verify address match
    // 3. Check timestamp validity
    return verified
}

LDAP Authentication

• Support Active Directory
• Organizational Unit (OU) mapping
• Attribute synchronization

PAM Authentication

• System account integration
• Support various PAM modules

Message Processing Pipeline

Incoming Mail → Anti-Spam Check → Virus Scan → Filter Rules
    ↓
Store to DB ← DKIM Signing ← Content Modification ← User Rules

Storage System

Database Layer

• User Data: Account information, quotas, settings
• Email Metadata: Sender, recipient, subject, timestamp
• Indexes: Fast search and retrieval

File Storage

• Maildir Format: One file per email
• Compression: Automatic compression of old emails
• S3-Compatible: Scalable to cloud storage

Data Flow

Sending Email Flow

1. Client connects (SMTP/Submission)
   ↓
2. Authentication verification
   ↓
3. Receive email content
   ↓
4. Verify recipients
   ↓
5. Apply filter rules
   ↓
6. DKIM signing
   ↓
7. Queue processing
   ↓
8. Send to target server

Receiving Email Flow

1. External server connects
   ↓
2. SPF/DKIM/DMARC checks
   ↓
3. Anti-spam checks
   ↓
4. Apply user rules (Sieve)
   ↓
5. Store to database
   ↓
6. Save email file
   ↓
7. Notify clients (IMAP IDLE)

Module System

Core Modules

• auth: Authentication providers
• storage: Storage backends
• filter: Email filtering
• modify: Content modification
• check: Validation checks

Extension Points

type Module interface {
    Name() string
    Init(config Config) error
    Process(ctx Context, msg *Message) error
}

Performance Optimization

Concurrency Model

• Goroutine Pools: Handle concurrent connections
• Async I/O: Non-blocking network operations
• Batch Processing: Database batch operations

Caching Strategy

• Authentication Cache: Reduce blockchain RPC calls
• User Data Cache: Frequently used data in memory cache
• DNS Cache: Reduce DNS queries

Connection Pooling

• Database Connection Pool: Reuse database connections
• RPC Connection Pool: Blockchain node connection reuse

Security Design

Multi-Layer Protection

1. Network Layer: TLS encryption
2. Authentication Layer: Multi-factor authentication support
3. Application Layer: Input validation, SQL injection protection
4. Data Layer: Encryption at rest

Rate Limiting

• Connection Rate: Prevent connection abuse
• Sending Rate: Prevent spam
• Authentication Attempts: Prevent brute force attacks

Scalability

Horizontal Scaling

           ┌─────────────┐
           │Load Balancer│
           └──────┬──────┘
                  │
        ┌─────────┼─────────┐
        ▼         ▼         ▼
    ┌──────┐  ┌──────┐  ┌──────┐
    │ Node │  │ Node │  │ Node │
    │  1   │  │  2   │  │  3   │
    └───┬──┘  └───┬──┘  └───┬──┘
        │         │         │
        └─────────┼─────────┘
                  ▼
         ┌────────────────┐
         │  Shared Storage│
         │  (Database/S3) │
         └────────────────┘

Component Separation

• Independent Deployment: SMTP, IMAP can be scaled separately
• Shared Storage: Multiple instances share data
• Load Balancing: Intelligent traffic distribution

Monitoring and Logging

Metrics Collection

• System Metrics: CPU, memory, disk
• Application Metrics: Email throughput, latency
• Business Metrics: User activity, storage usage

Logging System

Application Logs → Structured Output → Log Aggregation → Analytics Platform
                                        (ELK/Loki)

High Availability

Failover

• Master-Slave Replication: Database master-slave configuration
• Automatic Switching: Health checks and automatic failover
• Data Backup: Regular backups and recovery testing

Health Checks

type HealthCheck struct {
    Database  bool
    SMTP      bool
    IMAP      bool
    Storage   bool
}

---

For more technical details:

• Module System
• Performance Tuning
• Deployment Architecture