feat: implement comprehensive route-based email routing system

Replace legacy domain-rule based routing with flexible route-based system that supports:
- Multi-criteria matching (recipients, senders, IPs, authentication)
- Four action types (forward, process, deliver, reject)
- Moved DKIM signing to delivery phase for signature validity
- Connection pooling for efficient email forwarding
- Pattern caching for improved performance

This provides more granular control over email routing with priority-based matching and comprehensive test coverage.

ts/mail/routing/interfaces.ts

@@ -81,6 +81,43 @@ export interface IEmailAction {
     queue?: 'normal' | 'priority' | 'bulk';
   };
   
+  /** Options for various action types */
+  options?: {
+    /** MTA specific options */
+    mtaOptions?: {
+      domain?: string;
+      allowLocalDelivery?: boolean;
+      localDeliveryPath?: string;
+      dkimSign?: boolean;
+      dkimOptions?: {
+        domainName: string;
+        keySelector: string;
+        privateKey?: string;
+      };
+      smtpBanner?: string;
+      maxConnections?: number;
+      connTimeout?: number;
+      spoolDir?: string;
+    };
+    /** Content scanning configuration */
+    contentScanning?: boolean;
+    scanners?: Array<{
+      type: 'spam' | 'virus' | 'attachment';
+      threshold?: number;
+      action: 'tag' | 'reject';
+      blockedExtensions?: string[];
+    }>;
+    /** Email transformations */
+    transformations?: Array<{
+      type: string;
+      header?: string;
+      value?: string;
+      domains?: string[];
+      append?: boolean;
+      [key: string]: any;
+    }>;
+  };
+  
   /** Delivery options (applies to forward/process/deliver) */
   delivery?: {
     /** Rate limit (messages per minute) */