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.
