Advanced Dispatcher Patterns

Pattern 1: Offline Queue Dispatcher

Idea: Buffer failed emails to database, retry asynchronously.

public class OfflineQueueDispatcher : IEmailDispatcher
{
    public async Task SendAsync(...)
    {
        try
        {
            // Try main dispatcher
            return await _mainDispatcher.SendAsync(...);
        }
        catch
        {
            // Store in offline queue
            await _offlineQueueService.EnqueueAsync(message, ct);
            return EmailDispatchResult.Ok("queued");
        }
    }
}

Pattern 2: Logging Dispatcher

Idea: Log all emails to database/file before sending. Audit trail.

public class LoggingDispatcher : IEmailDispatcher
{
    public async Task SendAsync(...)
    {
        // Log email
        await _auditLog.LogAsync(new EmailAuditLog { 
            TenantID=metadata.TenantID, To=message.To, Subject=message.Subject 
        }, ct);
        
        // Send via main dispatcher
        return await _mainDispatcher.SendAsync(...);
    }
}

Pattern 3: Multi-Provider Router

Idea: Route to different providers based on email type or cost.

public class MultiProviderRouter : IEmailDispatcher
{
    public async Task SendAsync(...)
    {
        // Route based on subject/type
        var provider = message.Subject.Contains("urgent") ? "ses" : "smtp";
        var dispatcher = _factory.Get(provider);
        return await dispatcher.SendAsync(...);
    }
}

Pattern 4: IP Pooling Dispatcher

Idea: Distribute emails across multiple SES sending pools for reputation management.

public class IPPoolingDispatcher : IEmailDispatcher
{
    public async Task SendAsync(...)
    {
        // Select IP pool based on tenant/domain
        var pool = _ipPoolSelector.Select(message.To);
        var metadata = metadata with { IPPool = pool };
        return await _sesDispatcher.SendAsync(credential, metadata, message, ct);
    }
}

Pattern 5: Blockchain-Enabled Dispatcher

Idea: Log email hashes to blockchain for compliance/audit.

public class BlockchainDispatcher : IEmailDispatcher
{
    public async Task SendAsync(...)
    {
        // Send email
        var result = await _mainDispatcher.SendAsync(...);
        
        // Hash and log to blockchain
        if (result.Success)
        {
            var hash = Hash(message.Html + result.MessageID);
            await _blockchain.LogAsync(hash, ct);
        }
        
        return result;
    }
}

Pattern 6: Rate-Limited Dispatcher

Idea: Enforce per-tenant or per-recipient rate limits.

public class RateLimitedDispatcher : IEmailDispatcher
{
    public async Task SendAsync(...)
    {
        // Check rate limit: 100 emails/minute per tenant
        if (!await _rateLimiter.AllowAsync(metadata.TenantID, 100, 60, ct))
            return EmailDispatchResult.Fail("RATE_LIMIT", "Quota exceeded");
        
        return await _mainDispatcher.SendAsync(...);
    }
}

Next Steps

• Bring Your Own Provider — Implement custom dispatchers
• Sample JSON