Support for relaying mail.
| Class | DomainQueuer | An SMTP domain which add messages to a queue intended for relaying. |
| Class | RelayerMixin | No class docstring; 0/2 instance variables, 1/5 methods documented |
| Class | SMTPRelayer | A base class for SMTP relayers. |
| Class | ESMTPRelayer | A base class for ESMTP relayers. |