Zetian.Relay - SMTP Relay and Proxy Extension

SMTP relay and proxy extension for Zetian SMTP Server with smart host support, queue management, load balancing, and failover mechanisms.

⚡ Features

🎚️ Priority Queuing - Message priority support
📊 MX Routing - DNS MX record-based routing
🔀 Failover - Automatic failover to backup servers
📈 Queue Statistics - Real-time queue monitoring
💌 Bounce Messages - Automatic NDR generation
🎯 Domain Routing - Custom routing rules per domain
🌐 TLS/SSL - Secure connections with STARTTLS support
🔐 Authentication - Support for AUTH PLAIN and LOGIN
⏱️ Retry Logic - Exponential backoff with configurable limits
⚖️ Load Balancing - Distribute load across multiple relay servers
🔄 Queue Management - Persistent queue with retry mechanisms
📬 Smart Host Support - Route messages through configured relay servers

📦 Installation

# Install Zetian SMTP Server (required)
dotnet add package Zetian

# Install Relay Extension
dotnet add package Zetian.Relay

🚀 Quick Start

Basic Relay Setup

using Zetian.Server;
using Zetian.Relay.Extensions;

// Create SMTP server with relay enabled
var server = SmtpServerBuilder
    .CreateBasic()
    .EnableRelay();

// Start server with relay service
var relayService = await server.StartWithRelayAsync();

With Smart Host

using System.Net;
using Zetian.Server;
using Zetian.Relay.Extensions;
using Zetian.Relay.Configuration;

var server = SmtpServerBuilder
    .CreateBasic()
    .EnableRelay(config =>
    {
        config.DefaultSmartHost = new SmartHostConfiguration
        {
            Host = "smtp.example.com",
            Port = 587,
            Credentials = new NetworkCredential("user", "password"),
            UseTls = true
        };
    });

await server.StartAsync();

Multiple Smart Hosts with Failover

var server = SmtpServerBuilder
    .CreateBasic()
    .EnableRelay(config =>
{
    // Primary smart host
    config.DefaultSmartHost = new SmartHostConfiguration
    {
        Host = "primary.smtp.com",
        Port = 587,
        Priority = 10,
        Credentials = new NetworkCredential("user", "pass")
    };
    
    // Backup smart hosts
    config.SmartHosts.Add(new SmartHostConfiguration
    {
        Host = "backup1.smtp.com",
        Port = 587,
        Priority = 20,
        Credentials = new NetworkCredential("user", "pass")
    });
    
    config.SmartHosts.Add(new SmartHostConfiguration
    {
        Host = "backup2.smtp.com",
        Port = 587,
        Priority = 30
    });
});

🎯 Advanced Configuration

Using Relay Builder

using Zetian.Server;
using Zetian.Relay.Builder;
using Zetian.Relay.Extensions;

var relayConfig = new RelayBuilder()
    .WithSmartHost("smtp.office365.com", 587, "user@domain.com", "password")
    .MaxConcurrentDeliveries(20)
    .MaxRetries(5)
    .MessageLifetime(TimeSpan.FromDays(3))
    .ConnectionTimeout(TimeSpan.FromMinutes(10))
    .EnableTls(true, require: true)
    .LocalDomain("mail.mydomain.com")
    .AddLocalDomains("mydomain.com", "internal.local")
    .AddRelayDomains("partner.com", "customer.com")
    .RequireAuthentication(true)
    .EnableBounce(true, "postmaster@mydomain.com")
    .Build();

var server = SmtpServerBuilder
    .CreateBasic()
    .EnableRelay(relayConfig);

Domain-Specific Routing

var server = SmtpServerBuilder
    .CreateBasic()
    .EnableRelay(config =>
{
    // Route specific domains through different smart hosts
    config.DomainRouting["gmail.com"] = new SmartHostConfiguration
    {
        Host = "smtp.gmail.com",
        Port = 587,
        Credentials = new NetworkCredential("user@gmail.com", "app_password")
    };
    
    config.DomainRouting["outlook.com"] = new SmartHostConfiguration
    {
        Host = "smtp-mail.outlook.com",
        Port = 587,
        Credentials = new NetworkCredential("user@outlook.com", "password")
    };
    
    // Default for all other domains
    config.DefaultSmartHost = new SmartHostConfiguration
    {
        Host = "smtp.sendgrid.net",
        Port = 587,
        Credentials = new NetworkCredential("apikey", "SG.xxxxx")
    };
});

MX-Based Routing

var server = SmtpServerBuilder
    .CreateBasic()
    .EnableRelay(config =>
{
    // Use DNS MX records for routing
    config.UseMxRouting = true;
    
    // Optional: Custom DNS servers
    config.DnsServers.Add(IPAddress.Parse("8.8.8.8"));
    config.DnsServers.Add(IPAddress.Parse("1.1.1.1"));
    
    // Fallback smart host if MX lookup fails
    config.DefaultSmartHost = new SmartHostConfiguration
    {
        Host = "fallback.smtp.com",
        Port = 25
    };
});

Relay Networks Configuration

var server = SmtpServerBuilder
    .CreateBasic()
    .EnableRelay(config =>
{
    // Allow relay from specific IP addresses without authentication
    config.RelayNetworks.Add(IPAddress.Parse("192.168.1.0"));
    config.RelayNetworks.Add(IPAddress.Parse("10.0.0.0"));
    
    // Require authentication for all others
    config.RequireAuthentication = true;
});

📊 Queue Management

Manual Queue Operations

// Get relay service
var relayService = server.GetRelayService();

// Queue a message manually
var relayMessage = await server.QueueForRelayAsync(
    message,
    session,
    RelayPriority.High);

// Get queue statistics
var stats = await server.GetRelayStatisticsAsync();
Console.WriteLine($"Queued: {stats.QueuedMessages}");
Console.WriteLine($"In Progress: {stats.InProgressMessages}");
Console.WriteLine($"Delivered: {stats.DeliveredMessages}");
Console.WriteLine($"Failed: {stats.FailedMessages}");

// Get all messages in queue
var messages = await relayService.Queue.GetAllAsync();

// Get messages by status
var deferredMessages = await relayService.Queue.GetByStatusAsync(RelayStatus.Deferred);

// Remove a message
await relayService.Queue.RemoveAsync(queueId);

// Clear expired messages
var cleared = await relayService.Queue.ClearExpiredAsync();

Message Priority

server.MessageReceived += async (sender, e) =>
{
    // Determine priority based on sender or content
    var priority = e.Message.From?.Address?.EndsWith("@vip.com") == true
        ? RelayPriority.Urgent
        : RelayPriority.Normal;
    
    // Queue with priority
    await server.QueueForRelayAsync(e.Message, e.Session, priority);
};

🔄 Retry Configuration

var server = SmtpServerBuilder
    .CreateBasic()
    .EnableRelay(config =>
{
    // Maximum retry attempts
    config.MaxRetryCount = 10;
    
    // Message lifetime before expiration
    config.MessageLifetime = TimeSpan.FromDays(4);
    
    // Connection timeout per attempt
    config.ConnectionTimeout = TimeSpan.FromMinutes(5);
    
    // Queue processing interval
    config.QueueProcessingInterval = TimeSpan.FromSeconds(30);
    
    // Cleanup expired messages interval
    config.CleanupInterval = TimeSpan.FromHours(1);
});

Retry Schedule

The relay service uses exponential backoff for retries:

1st retry: 1 minute
2nd retry: 2 minutes
3rd retry: 4 minutes
4th retry: 8 minutes
5th retry: 16 minutes
6th retry: 32 minutes
7th+ retry: 1-4 hours (capped)

📬 Bounce Messages

var server = SmtpServerBuilder
    .CreateBasic()
    .EnableRelay(config =>
{
    // Enable bounce message generation
    config.EnableBounceMessages = true;
    
    // Set bounce sender address
    config.BounceSender = "postmaster@mydomain.com";
    
    // Enable delivery status notifications
    config.EnableDsn = true;
});

🔐 Authentication Methods

AUTH PLAIN

var smartHost = new SmartHostConfiguration
{
    Host = "smtp.example.com",
    Port = 587,
    Credentials = new NetworkCredential("username", "password"),
    UseStartTls = true
};

AUTH LOGIN

The relay client automatically detects and uses the appropriate authentication method based on server capabilities.

📈 Load Balancing

var server = SmtpServerBuilder
    .CreateBasic()
    .EnableRelay(config =>
{
    // Configure multiple smart hosts with weights
    config.SmartHosts.AddRange(new[]
    {
        new SmartHostConfiguration
        {
            Host = "smtp1.example.com",
            Port = 25,
            Priority = 10,
            Weight = 50  // 50% of traffic
        },
        new SmartHostConfiguration
        {
            Host = "smtp2.example.com",
            Port = 25,
            Priority = 10,
            Weight = 30  // 30% of traffic
        },
        new SmartHostConfiguration
        {
            Host = "smtp3.example.com",
            Port = 25,
            Priority = 10,
            Weight = 20  // 20% of traffic
        }
    });
});

🌐 TLS/SSL Configuration

var server = SmtpServerBuilder
    .CreateBasic()
    .EnableRelay(config =>
{
    // Enable TLS for outbound connections
    config.EnableTls = true;
    
    // Require TLS (fail if not available)
    config.RequireTls = true;
    
    // Configure SSL protocols
    config.SslProtocols = SslProtocols.Tls12 | SslProtocols.Tls13;
    
    // Validate server certificates
    config.ValidateServerCertificate = true;
});

🎛️ Extension Methods

// Create server first
var server = SmtpServerBuilder
    .CreateBasic()
    .EnableRelay();

// Add smart host
server.AddSmartHost("smtp.gmail.com", 587, 
    new NetworkCredential("user", "pass"));

// Set relay domains
server.SetRelayDomains("external.com", "partner.org");

// Set local domains (not relayed)
server.SetLocalDomains("mydomain.com", "internal.local");

// Add relay network
server.AddRelayNetwork(IPAddress.Parse("192.168.1.0"));

// Get relay statistics
var stats = await server.GetRelayStatisticsAsync();

// Get relay service
var relayService = server.GetRelayService();

🔍 Message Status

Status	Description
Queued	Message is waiting for delivery
InProgress	Message is currently being delivered
Delivered	Message successfully delivered
Failed	Permanent delivery failure
Deferred	Temporary failure, will retry
Expired	Message exceeded lifetime
Cancelled	Message was cancelled
PartiallyDelivered	Some recipients succeeded

📊 Monitoring

// Get comprehensive statistics
var stats = await relayService.Queue.GetStatisticsAsync();

Console.WriteLine($"Total Messages: {stats.TotalMessages}");
Console.WriteLine($"Queued: {stats.QueuedMessages}");
Console.WriteLine($"In Progress: {stats.InProgressMessages}");
Console.WriteLine($"Deferred: {stats.DeferredMessages}");
Console.WriteLine($"Delivered: {stats.DeliveredMessages}");
Console.WriteLine($"Failed: {stats.FailedMessages}");
Console.WriteLine($"Expired: {stats.ExpiredMessages}");
Console.WriteLine($"Total Size: {stats.TotalSize} bytes");
Console.WriteLine($"Oldest Message: {stats.OldestMessageTime}");
Console.WriteLine($"Average Queue Time: {stats.AverageQueueTime}");
Console.WriteLine($"Average Retry Count: {stats.AverageRetryCount}");

// Messages by priority
foreach (var kvp in stats.MessagesByPriority)
{
    Console.WriteLine($"Priority {kvp.Key}: {kvp.Value} messages");
}

// Messages by smart host
foreach (var kvp in stats.MessagesBySmartHost)
{
    Console.WriteLine($"Host {kvp.Key}: {kvp.Value} messages");
}

🚀 Performance Tips

DNS Caching - Cache MX record lookups
Connection Pooling - Reuse SMTP client connections
Message Batching - Group messages to same destination
Queue Persistence - Consider persistent queue for reliability
Smart Host Selection - Use priority and weight for optimal routing
Concurrent Deliveries - Adjust MaxConcurrentDeliveries based on resources

📚 Best Practices

Log Relay Activity - Audit trail for compliance
Implement Rate Limiting - Prevent abuse of relay
Monitor Queue Size - Prevent unbounded growth
Use TLS When Possible - Secure message transmission
Configure Bounce Handling - Inform senders of failures
Regular Cleanup - Remove expired messages periodically
Set Message Lifetime - Clean up undeliverable messages
Always Configure Timeouts - Prevent hanging connections

🔒 Security Considerations

Regular security audits
Monitor for relay abuse
Implement rate limiting
Validate server certificates
Limit relay networks to trusted IPs
Use TLS/SSL for all outbound connections
Always require authentication for relay access

📋 Requirements

Windows, Linux, or macOS
.NET 6.0, 7.0, 8.0, 9.0, or 10.0
Zetian SMTP Server package

📚 Documentation & Support

Issues: GitHub Issues
Examples: GitHub Examples
Discussions: GitHub Discussions
Documentation: Zetian Documentation

📄 License

MIT License - see LICENSE

Built with ❤️ for the .NET community

Zetian.Relay - SMTP Relay and Proxy Extension

SMTP relay and proxy extension for Zetian SMTP Server with smart host support, queue management, load balancing, and failover mechanisms.

⚡ Features

🎚️ Priority Queuing - Message priority support
📊 MX Routing - DNS MX record-based routing
🔀 Failover - Automatic failover to backup servers
📈 Queue Statistics - Real-time queue monitoring
💌 Bounce Messages - Automatic NDR generation
🎯 Domain Routing - Custom routing rules per domain
🌐 TLS/SSL - Secure connections with STARTTLS support
🔐 Authentication - Support for AUTH PLAIN and LOGIN
⏱️ Retry Logic - Exponential backoff with configurable limits
⚖️ Load Balancing - Distribute load across multiple relay servers
🔄 Queue Management - Persistent queue with retry mechanisms
📬 Smart Host Support - Route messages through configured relay servers

📦 Installation

# Install Zetian SMTP Server (required)
dotnet add package Zetian

# Install Relay Extension
dotnet add package Zetian.Relay

🚀 Quick Start

Basic Relay Setup

using Zetian.Server;
using Zetian.Relay.Extensions;

// Create SMTP server with relay enabled
var server = SmtpServerBuilder
    .CreateBasic()
    .EnableRelay();

// Start server with relay service
var relayService = await server.StartWithRelayAsync();

With Smart Host

using System.Net;
using Zetian.Server;
using Zetian.Relay.Extensions;
using Zetian.Relay.Configuration;

var server = SmtpServerBuilder
    .CreateBasic()
    .EnableRelay(config =>
    {
        config.DefaultSmartHost = new SmartHostConfiguration
        {
            Host = "smtp.example.com",
            Port = 587,
            Credentials = new NetworkCredential("user", "password"),
            UseTls = true
        };
    });

await server.StartAsync();

Multiple Smart Hosts with Failover

var server = SmtpServerBuilder
    .CreateBasic()
    .EnableRelay(config =>
{
    // Primary smart host
    config.DefaultSmartHost = new SmartHostConfiguration
    {
        Host = "primary.smtp.com",
        Port = 587,
        Priority = 10,
        Credentials = new NetworkCredential("user", "pass")
    };
    
    // Backup smart hosts
    config.SmartHosts.Add(new SmartHostConfiguration
    {
        Host = "backup1.smtp.com",
        Port = 587,
        Priority = 20,
        Credentials = new NetworkCredential("user", "pass")
    });
    
    config.SmartHosts.Add(new SmartHostConfiguration
    {
        Host = "backup2.smtp.com",
        Port = 587,
        Priority = 30
    });
});

🎯 Advanced Configuration

Using Relay Builder

using Zetian.Server;
using Zetian.Relay.Builder;
using Zetian.Relay.Extensions;

var relayConfig = new RelayBuilder()
    .WithSmartHost("smtp.office365.com", 587, "user@domain.com", "password")
    .MaxConcurrentDeliveries(20)
    .MaxRetries(5)
    .MessageLifetime(TimeSpan.FromDays(3))
    .ConnectionTimeout(TimeSpan.FromMinutes(10))
    .EnableTls(true, require: true)
    .LocalDomain("mail.mydomain.com")
    .AddLocalDomains("mydomain.com", "internal.local")
    .AddRelayDomains("partner.com", "customer.com")
    .RequireAuthentication(true)
    .EnableBounce(true, "postmaster@mydomain.com")
    .Build();

var server = SmtpServerBuilder
    .CreateBasic()
    .EnableRelay(relayConfig);

Domain-Specific Routing

var server = SmtpServerBuilder
    .CreateBasic()
    .EnableRelay(config =>
{
    // Route specific domains through different smart hosts
    config.DomainRouting["gmail.com"] = new SmartHostConfiguration
    {
        Host = "smtp.gmail.com",
        Port = 587,
        Credentials = new NetworkCredential("user@gmail.com", "app_password")
    };
    
    config.DomainRouting["outlook.com"] = new SmartHostConfiguration
    {
        Host = "smtp-mail.outlook.com",
        Port = 587,
        Credentials = new NetworkCredential("user@outlook.com", "password")
    };
    
    // Default for all other domains
    config.DefaultSmartHost = new SmartHostConfiguration
    {
        Host = "smtp.sendgrid.net",
        Port = 587,
        Credentials = new NetworkCredential("apikey", "SG.xxxxx")
    };
});

MX-Based Routing

var server = SmtpServerBuilder
    .CreateBasic()
    .EnableRelay(config =>
{
    // Use DNS MX records for routing
    config.UseMxRouting = true;
    
    // Optional: Custom DNS servers
    config.DnsServers.Add(IPAddress.Parse("8.8.8.8"));
    config.DnsServers.Add(IPAddress.Parse("1.1.1.1"));
    
    // Fallback smart host if MX lookup fails
    config.DefaultSmartHost = new SmartHostConfiguration
    {
        Host = "fallback.smtp.com",
        Port = 25
    };
});

Relay Networks Configuration

var server = SmtpServerBuilder
    .CreateBasic()
    .EnableRelay(config =>
{
    // Allow relay from specific IP addresses without authentication
    config.RelayNetworks.Add(IPAddress.Parse("192.168.1.0"));
    config.RelayNetworks.Add(IPAddress.Parse("10.0.0.0"));
    
    // Require authentication for all others
    config.RequireAuthentication = true;
});

📊 Queue Management

Manual Queue Operations

// Get relay service
var relayService = server.GetRelayService();

// Queue a message manually
var relayMessage = await server.QueueForRelayAsync(
    message,
    session,
    RelayPriority.High);

// Get queue statistics
var stats = await server.GetRelayStatisticsAsync();
Console.WriteLine($"Queued: {stats.QueuedMessages}");
Console.WriteLine($"In Progress: {stats.InProgressMessages}");
Console.WriteLine($"Delivered: {stats.DeliveredMessages}");
Console.WriteLine($"Failed: {stats.FailedMessages}");

// Get all messages in queue
var messages = await relayService.Queue.GetAllAsync();

// Get messages by status
var deferredMessages = await relayService.Queue.GetByStatusAsync(RelayStatus.Deferred);

// Remove a message
await relayService.Queue.RemoveAsync(queueId);

// Clear expired messages
var cleared = await relayService.Queue.ClearExpiredAsync();

Message Priority

server.MessageReceived += async (sender, e) =>
{
    // Determine priority based on sender or content
    var priority = e.Message.From?.Address?.EndsWith("@vip.com") == true
        ? RelayPriority.Urgent
        : RelayPriority.Normal;
    
    // Queue with priority
    await server.QueueForRelayAsync(e.Message, e.Session, priority);
};

🔄 Retry Configuration

var server = SmtpServerBuilder
    .CreateBasic()
    .EnableRelay(config =>
{
    // Maximum retry attempts
    config.MaxRetryCount = 10;
    
    // Message lifetime before expiration
    config.MessageLifetime = TimeSpan.FromDays(4);
    
    // Connection timeout per attempt
    config.ConnectionTimeout = TimeSpan.FromMinutes(5);
    
    // Queue processing interval
    config.QueueProcessingInterval = TimeSpan.FromSeconds(30);
    
    // Cleanup expired messages interval
    config.CleanupInterval = TimeSpan.FromHours(1);
});

Retry Schedule

The relay service uses exponential backoff for retries:

1st retry: 1 minute
2nd retry: 2 minutes
3rd retry: 4 minutes
4th retry: 8 minutes
5th retry: 16 minutes
6th retry: 32 minutes
7th+ retry: 1-4 hours (capped)

📬 Bounce Messages

var server = SmtpServerBuilder
    .CreateBasic()
    .EnableRelay(config =>
{
    // Enable bounce message generation
    config.EnableBounceMessages = true;
    
    // Set bounce sender address
    config.BounceSender = "postmaster@mydomain.com";
    
    // Enable delivery status notifications
    config.EnableDsn = true;
});

🔐 Authentication Methods

AUTH PLAIN

var smartHost = new SmartHostConfiguration
{
    Host = "smtp.example.com",
    Port = 587,
    Credentials = new NetworkCredential("username", "password"),
    UseStartTls = true
};

AUTH LOGIN

The relay client automatically detects and uses the appropriate authentication method based on server capabilities.

📈 Load Balancing

var server = SmtpServerBuilder
    .CreateBasic()
    .EnableRelay(config =>
{
    // Configure multiple smart hosts with weights
    config.SmartHosts.AddRange(new[]
    {
        new SmartHostConfiguration
        {
            Host = "smtp1.example.com",
            Port = 25,
            Priority = 10,
            Weight = 50  // 50% of traffic
        },
        new SmartHostConfiguration
        {
            Host = "smtp2.example.com",
            Port = 25,
            Priority = 10,
            Weight = 30  // 30% of traffic
        },
        new SmartHostConfiguration
        {
            Host = "smtp3.example.com",
            Port = 25,
            Priority = 10,
            Weight = 20  // 20% of traffic
        }
    });
});

🌐 TLS/SSL Configuration

var server = SmtpServerBuilder
    .CreateBasic()
    .EnableRelay(config =>
{
    // Enable TLS for outbound connections
    config.EnableTls = true;
    
    // Require TLS (fail if not available)
    config.RequireTls = true;
    
    // Configure SSL protocols
    config.SslProtocols = SslProtocols.Tls12 | SslProtocols.Tls13;
    
    // Validate server certificates
    config.ValidateServerCertificate = true;
});

🎛️ Extension Methods

// Create server first
var server = SmtpServerBuilder
    .CreateBasic()
    .EnableRelay();

// Add smart host
server.AddSmartHost("smtp.gmail.com", 587, 
    new NetworkCredential("user", "pass"));

// Set relay domains
server.SetRelayDomains("external.com", "partner.org");

// Set local domains (not relayed)
server.SetLocalDomains("mydomain.com", "internal.local");

// Add relay network
server.AddRelayNetwork(IPAddress.Parse("192.168.1.0"));

// Get relay statistics
var stats = await server.GetRelayStatisticsAsync();

// Get relay service
var relayService = server.GetRelayService();

🔍 Message Status

Status	Description
Queued	Message is waiting for delivery
InProgress	Message is currently being delivered
Delivered	Message successfully delivered
Failed	Permanent delivery failure
Deferred	Temporary failure, will retry
Expired	Message exceeded lifetime
Cancelled	Message was cancelled
PartiallyDelivered	Some recipients succeeded

📊 Monitoring

// Get comprehensive statistics
var stats = await relayService.Queue.GetStatisticsAsync();

Console.WriteLine($"Total Messages: {stats.TotalMessages}");
Console.WriteLine($"Queued: {stats.QueuedMessages}");
Console.WriteLine($"In Progress: {stats.InProgressMessages}");
Console.WriteLine($"Deferred: {stats.DeferredMessages}");
Console.WriteLine($"Delivered: {stats.DeliveredMessages}");
Console.WriteLine($"Failed: {stats.FailedMessages}");
Console.WriteLine($"Expired: {stats.ExpiredMessages}");
Console.WriteLine($"Total Size: {stats.TotalSize} bytes");
Console.WriteLine($"Oldest Message: {stats.OldestMessageTime}");
Console.WriteLine($"Average Queue Time: {stats.AverageQueueTime}");
Console.WriteLine($"Average Retry Count: {stats.AverageRetryCount}");

// Messages by priority
foreach (var kvp in stats.MessagesByPriority)
{
    Console.WriteLine($"Priority {kvp.Key}: {kvp.Value} messages");
}

// Messages by smart host
foreach (var kvp in stats.MessagesBySmartHost)
{
    Console.WriteLine($"Host {kvp.Key}: {kvp.Value} messages");
}

🚀 Performance Tips

DNS Caching - Cache MX record lookups
Connection Pooling - Reuse SMTP client connections
Message Batching - Group messages to same destination
Queue Persistence - Consider persistent queue for reliability
Smart Host Selection - Use priority and weight for optimal routing
Concurrent Deliveries - Adjust MaxConcurrentDeliveries based on resources

📚 Best Practices

Log Relay Activity - Audit trail for compliance
Implement Rate Limiting - Prevent abuse of relay
Monitor Queue Size - Prevent unbounded growth
Use TLS When Possible - Secure message transmission
Configure Bounce Handling - Inform senders of failures
Regular Cleanup - Remove expired messages periodically
Set Message Lifetime - Clean up undeliverable messages
Always Configure Timeouts - Prevent hanging connections

🔒 Security Considerations

Regular security audits
Monitor for relay abuse
Implement rate limiting
Validate server certificates
Limit relay networks to trusted IPs
Use TLS/SSL for all outbound connections
Always require authentication for relay access

📋 Requirements

Windows, Linux, or macOS
.NET 6.0, 7.0, 8.0, 9.0, or 10.0
Zetian SMTP Server package

📚 Documentation & Support

Issues: GitHub Issues
Examples: GitHub Examples
Discussions: GitHub Discussions
Documentation: Zetian Documentation

📄 License

MIT License - see LICENSE

Built with ❤️ for the .NET community

Soferity/Zetian.Relayv1.0.5

Get Started

Readme

Zetian.Relay - SMTP Relay and Proxy Extension

⚡ Features

📦 Installation

🚀 Quick Start

Basic Relay Setup

With Smart Host

Multiple Smart Hosts with Failover

🎯 Advanced Configuration

Using Relay Builder

Domain-Specific Routing

MX-Based Routing

Relay Networks Configuration

📊 Queue Management

Manual Queue Operations

Message Priority

🔄 Retry Configuration

Retry Schedule

📬 Bounce Messages

🔐 Authentication Methods

AUTH PLAIN

AUTH LOGIN

📈 Load Balancing

🌐 TLS/SSL Configuration

🎛️ Extension Methods

🔍 Message Status

📊 Monitoring

🚀 Performance Tips

📚 Best Practices

🔒 Security Considerations

📋 Requirements

📚 Documentation & Support

📄 License

Soferity/Zetian.Relayv1.0.5

Get Started

Readme

Zetian.Relay - SMTP Relay and Proxy Extension

⚡ Features

📦 Installation

🚀 Quick Start

Basic Relay Setup

With Smart Host

Multiple Smart Hosts with Failover

🎯 Advanced Configuration

Using Relay Builder

Domain-Specific Routing

MX-Based Routing

Relay Networks Configuration

📊 Queue Management

Manual Queue Operations

Message Priority

🔄 Retry Configuration

Retry Schedule

📬 Bounce Messages

🔐 Authentication Methods

AUTH PLAIN

AUTH LOGIN

📈 Load Balancing

🌐 TLS/SSL Configuration

🎛️ Extension Methods

🔍 Message Status

📊 Monitoring

🚀 Performance Tips

📚 Best Practices

🔒 Security Considerations

📋 Requirements

📚 Documentation & Support

📄 License