DNS lookup MTA options

In addition to the   and     MTA options with some DNS lookup effects, see also  TCP/IP channels for additional, but channel-specific, DNS-related options. And see SPF MTA options for DNS SPF lookup MTA options.

See also:
 * blocked_mail_from_ips MTA Option
 * return_envelope MTA Option
 * TCPIP channels
 * SPF MTA options
 * MTA options