Mail service support.
| Class | DomainWithDefaultDict | A simulated dictionary for mapping domain names to domain objects with a default value for non-existing keys. |
| Class | BounceDomain | A domain with no users. |
| Class | FileMessage | A message receiver which delivers a message to a file. |
| Class | MailService | An email service. |
| Class | FileMonitoringService | A service for monitoring changes to files. |