Configuration

Configure Zetian SMTP Server according to your needs.

Fluent Builder Pattern

Zetian uses fluent builder pattern for readable and chainable configuration. You can configure all settings in a single expression.

Basic Configuration

Configure your server with SmtpServerBuilder:

ServerConfiguration.cs

using Zetian;

var server = new SmtpServerBuilder()
    // Basic Settings
    .Port(587)                           // Port number
    .ServerName("My SMTP Server")        // Server name
    .MaxMessageSizeMB(25)                // Max message size (MB)
    .MaxRecipients(100)                  // Max number of recipients
    .MaxConnections(50)                  // Max number of connections
    .MaxConnectionsPerIP(10)             // Max connections per IP
    
    // Security
    .RequireAuthentication()             // Authentication required
    .RequireSecureConnection()           // TLS/SSL required
    .Certificate("cert.pfx", "password") // SSL certificate
    
    // SMTP Features
    .EnableSmtpUtf8()                    // UTF-8 support
    .EnablePipelining()                  // Pipeline support
    
    // Timeout Settings
    .ConnectionTimeout(TimeSpan.FromMinutes(5))
    .CommandTimeout(TimeSpan.FromSeconds(30))
    
    .Build();

Basic Settings

• Port - SMTP port number
• ServerName - Server name
• MaxMessageSizeMB - Max message size
• MaxRecipients - Max number of recipients

Connection Limits

• MaxConnections - Total connection limit
• MaxConnectionsPerIP - Limit per IP
• ConnectionTimeout - Connection timeout
• CommandTimeout - Command timeout

Authentication Configuration

Configure different authentication methods:

AuthConfiguration.cs

// Simple authentication
.SimpleAuthentication("admin", "password123")

// Custom authentication
.AuthenticationHandler(async (username, password) =>
{
    // Database check
    var user = await GetUserAsync(username);
    if (user != null && VerifyPassword(password, user.PasswordHash))
    {
        return AuthenticationResult.Succeed(username);
    }
    return AuthenticationResult.Fail("Invalid credentials");
})

// Multiple authentication mechanisms
.AddAuthenticationMechanism("PLAIN")
.AddAuthenticationMechanism("LOGIN")

PLAIN Auth

Simple username/password

Legacy auth

Custom Auth

Custom handler

Filtering Configuration

Two different filtering approaches:

FilterConfiguration.cs

// Protocol-Level Filtering (at SMTP command level)
var server = new SmtpServerBuilder()
    .Port(25)
    // Domain filtering
    .WithSenderDomainWhitelist("trusted.com", "partner.org")
    .WithSenderDomainBlacklist("spam.com", "junk.org")
    .WithRecipientDomainWhitelist("mydomain.com")
    
    // Message size limit
    .MaxMessageSizeMB(10)
    
    // Message storage
    .WithFileMessageStore(@"C:\smtp_messages", createDateFolders: true)
    .Build();

// Event-Based Filtering (after message is received)
server.AddSpamFilter(new[] { "spam.com", "junk.org" });
server.AddSizeFilter(10 * 1024 * 1024); // 10MB
server.AddAllowedDomains("example.com");

Protocol-Level Filtering

Early rejection during SMTP commands. More efficient, saves bandwidth.

• At MAIL FROM/RCPT TO level
• Bandwidth savings
• Fast rejection

Event-Based Filtering

Filtering after message is received. More flexible, can check content.

• Full message content check
• Complex logic support
• Dynamic filters

Rate Limiting

Speed limiting for spam protection:

RateLimiting.cs

using Zetian.Extensions;
using Zetian.Extensions.RateLimiting;

// Rate limiting configuration
var rateLimitConfig = new RateLimitConfiguration
{
    MaxRequests = 100,             // Maximum number of requests
    UseSlidingWindow = false,      // Fixed or sliding window
    Window = TimeSpan.FromHours(1) // Time window
};

server.AddRateLimiting(rateLimitConfig);

// Alternative: Ready-made configurations
server.AddRateLimiting(RateLimitConfiguration.PerDay(1000));  // 1000 per day
server.AddRateLimiting(RateLimitConfiguration.PerHour(100));  // 100 per hour
server.AddRateLimiting(RateLimitConfiguration.PerMinute(10)); // 10 per minute

Important Note

Rate limiting works based on IP. Be careful in localhost tests. You can keep limits high in development environment.

Authentication →

Security and authentication details