RE: Duplicate zone found.
Something is misconfigured with the DNS config, obviously, but I will not
speculate what it is. Did you let the DNS admins know (give them the dnsreport
info you have below) and are they investigating?

RE: email blocking
Any mail server configured to check for the validity of a connecting SMTP
server's PTR record will reject the connection if it cannot find one.
See RFC1123 and RFC1912 about a legitimate MTA having a PTR record.
It's a great way to limit email abuse.

Fixing the rDNS issue may fix the email issue. Regardless, it will be time well
spent as it may haunt you until it is fixed.


--- andrewgroups@gmail.com wrote:

> When I run a reverse DNS search on our hosting provider, this error
> "WARNING: Duplicate zone found ..." appears randomly. Some email
> server are blocking us and I suspect it is because they have something
> that is not well configured. Can anyone figure out what the problem is
> and why this "Duplicate zone found" error is returned?
> Preparation:
> The reverse DNS entry for an IP is found by reversing the IP, adding
> it to "in-addr.arpa", and looking up the PTR record.
> So, the reverse DNS entry for is found by looking up the
> PTR record for
> All DNS requests start by asking the root servers, and they let us know
> what to do next.
> See How Reverse DNS Lookups Work for more information.
> How I am searching:
> Asking i.root-servers.net for PTR record:
> i.root-servers.net says to go to figwort.arin.net. (zone:
> 216.in-addr.arpa.)
> Asking figwort.arin.net. for PTR record:
> figwort.arin.net [] says to go to
> dns-01-002.root-dns.com. (zone: 255.133.216.in-addr.arpa.)
> Asking dns-01-002.root-dns.com. for PTR
> record:
> dns-01-002.root-dns.com [] says to go to
> dns-01-001.root-dns.com. (zone: 255.133.216.in-addr.arpa.)
> WARNING: Duplicate zone found (zone 255.133.216.in-addr.arpa. is
> repeated). This can prevent the lookup from continuing
> (BIND8 and BIND9 will cause a 'server failure' response).
> Although I will continue, be aware that
> most DNS servers will not see your reverse DNS entry.
> Asking dns-01-001.root-dns.com. for PTR
> record: Got CNAME referral to 56.0/ at
> server dns-01-001.root-dns.com. (zone 0/
> [from]
> Asking d.root-servers.net for 56.0/ PTR
> record:
> d.root-servers.net [] says to go to henna.ARIN.NET.
> (zone: 216.in-addr.arpa.)
> Asking henna.ARIN.NET. for 56.0/ PTR
> record:
> henna.arin.net [] says to go to
> dns-01-001.root-dns.com. (zone: 255.133.216.in-addr.arpa.)
> Asking dns-01-001.root-dns.com. for 56.0/
> PTR record: Reports NET-allocation-00025443.ix.sitestream.net. [from
> Answer:
> PTR record: NET-allocation-00025443.ix.sitestream.net.
> [TTL 86400s] [A=None] *ERROR* There is no A record for
> NET-allocation-00025443.ix.sitestream.net. (may be negatively cached).
> To see the reverse DNS traversal, to make sure that all DNS servers are
> reporting the correct results, you can Click Here.