`relay`: `<string>` ::

The default mail delivery transport (incoming mails).

`relaynomx`: `<boolean>` ('default =' `0`)::

Disable MX lookups for default relay.

`relayport`: `<integer> (1 - 65535)` ('default =' `25`)::

SMTP port number for relay host.

`smarthost`: `<string>` ::

When set, all outgoing mails are deliverd to the specified smarthost.

`smarthostport`: `<integer> (1 - 65535)` ('default =' `25`)::

SMTP port number for smarthost.