mail.pgdg.com has one IP number , but the reverse is 50.142.96.66.static.eigbox.net. mx.hitt.com, mx.iapl.net, mx.jnvr.net, mx.kuan.com, mx.mvcs.net and at least 100 other hosts point to the same IP. pgdg.com use this as a mailserver. pgdg.com is delegated to two nameservers, however both delegated nameservers are missing in the zone and one other nameserver is listed. Two nameservers have the same IP number. Some of them are on the same IP network. Incoming mail for pgdg.com is handled by one mailserver at pgdg.com themselves. mail.pgdg.com is hosted on a server in United States.