Hi Recently I have installed Mail Server in my Ubuntu Machine (MTA - postfix , MDA - Courirer , Client - Squirrelmail and outlook) And configured DNS too. But when i tried to send a mail to yahoo my mail.log message shows an error saying that Jul 15 20:22:00 ityug postfix/smtp: 348CED00444: host b.mx.mail.yahoo.com[220.127.116.11] refused to talk to me: 553 Mail from 18.104.22.168 not allowed - 5.7.1 [BL21] [B]Connections not accepted from IP addresses on Spamhaus PBL;[/U][/B] see http://postmaster.yahoo.com/550-bl21.html  How to overcome this PBL error? And I tried nslookup my ip address it is redirecting to my ISP domain it is not showing my domain . why ? Server: 10.0.0.1 Address: 10.0.0.1#53 Non-authoritative answer: 22.214.171.124.in-addr.arpa name = ABTS-AP-Static-092.248.169.122.airtelbroadband.in. Authoritative answers can be found from: 248.169.122.in-addr.arpa nameserver = dnsglobal.mantraonline.com. 248.169.122.in-addr.arpa nameserver = dnsbom.mantraonline.com. 248.169.122.in-addr.arpa nameserver = dnsdel.mantraonline.com. 248.169.122.in-addr.arpa nameserver = aaadel.mantraonline.com. 248.169.122.in-addr.arpa nameserver = dnsblr.mantraonline.com. aaadel.mantraonline.com internet address = 126.96.36.199 dnsblr.mantraonline.com internet address = 188.8.131.52 dnsbom.mantraonline.com internet address = 184.108.40.206 dnsdel.mantraonline.com internet address = 220.127.116.11 dnsglobal.mantraonline.com internet address = 18.104.22.168 Any body suggest me where I did the mistake ?