test(dns): add comprehensive tests for DNS record creation

- Add test.dns-manager-creation.ts to verify DNS record creation
- Test MX, SPF, DMARC, and DKIM record registration
- Verify records are stored in StorageManager
- Update readme.hints.md with DNS architecture refactoring notes

readme.hints.md

@@ -835,4 +835,48 @@ Rate limiting is now fully integrated into SMTP server handlers:
 The only remaining item is implementing hour/day rate limits in the UnifiedRateLimiter, which would require:
 1. Additional counters for hourly and daily windows
 2. Separate tracking for these longer time periods
-3. Cleanup logic for expired hourly/daily counters
+3. Cleanup logic for expired hourly/daily counters
+
+## DNS Architecture Refactoring (2025-05-30) - COMPLETED
+
+### Overview
+The DNS functionality has been refactored from UnifiedEmailServer to a dedicated DnsManager class for better discoverability and separation of concerns.
+
+### Key Changes
+1. **Renamed DnsValidator to DnsManager:**
+   - Extended functionality to handle both validation and creation of DNS records
+   - Added `ensureDnsRecords()` as the main entry point
+   - Moved DNS record creation logic from UnifiedEmailServer
+
+2. **DnsManager Responsibilities:**
+   - Validate DNS configuration for all modes (forward, internal-dns, external-dns)
+   - Create DNS records for internal-dns domains
+   - Create DKIM records for all domains (when DKIMCreator is provided)
+   - Store DNS records in StorageManager for persistence
+
+3. **DNS Record Creation Flow:**
+   ```typescript
+   // In UnifiedEmailServer
+   const dnsManager = new DnsManager(this.dcRouter);
+   await dnsManager.ensureDnsRecords(domainConfigs, this.dkimCreator);
+   ```
+
+4. **Testing Pattern for DNS:**
+   - Mock the DNS server in tests by providing a mock `registerHandler` function
+   - Store handlers in a Map with key format: `${domain}:${types.join(',')}`
+   - Retrieve handlers with key format: `${domain}:${type}`
+   - Example mock implementation:
+   ```typescript
+   this.dnsServer = {
+     registerHandler: (name: string, types: string[], handler: () => any) => {
+       const key = `${name}:${types.join(',')}`;
+       this.dnsHandlers.set(key, handler);
+     }
+   };
+   ```
+
+### Benefits
+- DNS functionality is now easily discoverable in DnsManager
+- Clear separation between DNS management and email server logic
+- UnifiedEmailServer is simpler and more focused
+- All DNS-related tests pass successfully