- 2013-05-11 修正
# main.cf smtp_dns_support_level = disabled
# /etc/nsswitch.conf hosts: files dns
ドキュメントでは次のように記載されている。 「"native" lookup」の詳細については、smtp_host_lookupの項に説明がある。
smtp_dns_support_level (default: empty) Level of DNS support in the Postfix SMTP client. With "smtp_dns_support_level" left at its empty default value, the legacy "disable_dns_lookups" parameter controls whether DNS is enabled in the Postfix SMTP client, otherwise the legacy parameter is ignored. Specify one of the following: disabled Disable DNS lookups. No MX lookups are performed and hostname to address lookups are unconditionally "native". This setting is not appropriate for hosts that deliver mail to the public Internet. Some obsolete how-to documents recommend disabling DNS lookups in some configurations with content_filters. This is no longer required and strongly discouraged. enabled Enable DNS lookups. Nexthop destination domains not enclosed in "" will be subject to MX lookups. If "dns" and "native" are included in the "smtp_host_lookup" parameter value, DNS will be queried first to resolve MX-host A records, followed by "native" lookups if no answer is found in DNS. dnssec Enable DNSSEC lookups. The "dnssec" setting differs from the "enabled" setting above in the following ways: * Any MX lookups will set RES_USE_DNSSEC and RES_USE_EDNS0 to request DNSSEC-validated responses. If the MX response is DNSSEC-validated the corresponding hostnames are considered validated. * The address lookups of validated hostnames are also validated, (provided of course "smtp_host_lookup" includes "dns", see below). * Temporary failures in DNSSEC-enabled hostname-to-address resolution block any "native" lookups. Additional "native" lookups only happen when DNSSEC lookups hard-fail (NODATA or NXDOMAIN).
smtp_host_lookup (default: dns) What mechanisms the Postfix SMTP client uses to look up a host's IP address. This parameter is ignored when DNS lookups are disabled (see: disable_dns_lookups and smtp_dns_support_level). The "dns" mechanism is always tried before "native" if both are listed. Specify one of the following: dns Hosts can be found in the DNS (preferred). native Use the native naming service only (nsswitch.conf, or equivalent mechanism). dns, native Use the native service for hosts not found in the DNS. This feature is available in Postfix 2.1 and later.