#!/bin/sh

IP=$(curl ifconfig.me)
curl_retval=$?
host_answer=$(host "$IP")
rev_dns="${host_answer##* }"
rev_dns="${rev_dns%.}"

echo "Rev. DNS is: $rev_dns"

sed -e "s/^myhostname.*/myhostname = $rev_dns ses/" /etc/postfix/main.cf

echo $curl_retval