Issue with AT&T IPs?

Barry S. Finkel bsfinkel at
Tue Dec 5 19:21:35 UTC 2017

On 12/5/2017 "Lightner, Jeffrey"<JLightner at> wrote:
> We're having issues send email to a user @SIDDHAFLOWERS.COM
> Investigation here shows that the issue we have is querying your name servers (both by name and by IP) are refusing to respond to our name servers.
> Their name servers:
> Our name servers:
> We find other name servers such as those as Google are able to query their name servers.   Based on that I determined their name server IP (for both) is   However, if I attempt to reach port 53 (DNS) on that IP from our name servers it simply fails to connect.   Our Network Security engineer did a capture and shows we send packets but never get a response.
> Interestingly further testing shows this is an issue from any of our AT&T provided IPs:
> But not from separate QTS Datacenter provided IPs:
> I've reached out to the folks at QuickFix and am waiting to hear back but we've seen a similar issue on another domain using separate name servers.    Is it possible there is some sort of blacklist for DNS (not email) that people might be subscribing to that would cause them to block AT&T IPs?  We can do queries from our DNS to most domains but have identified these 2 as problems so suspect there might be others.
> By the way, I can reach their mail server via command line connection to port 25 on its IP.   The issue here is purely in querying the DNS servers which of course means mail programs can't determine the MX records themselves.
> Last night I did see some posts suggesting commenting out query-source but testing that didn't do anything.   We do have our query-source setup for random outbound ports and I verified last night that it still works based on the test site for that.
> Most of what I find about blacklisting is about spam blacklisting of mail servers not blacklisting of DNS server queries and it is the latter we are experiencing.
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Here is a query I just did:

D:\>dig SIDDHAFLOWERS.COM mx @ns1.quickfix8.COM.

; <<>> DiG 9.9.3-P1 <<>> SIDDHAFLOWERS.COM mx @ns1.quickfix8.COM.
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 63456
;; flags: qr aa rd; QUERY: 1, ANSWER: 7, AUTHORITY: 2, ADDITIONAL: 3
;; WARNING: recursion requested but not available

; EDNS: version: 0, flags:; udp: 4096
;SIDDHAFLOWERS.COM.             IN      MX

SIDDHAFLOWERS.COM.      14400   IN      MX      1
SIDDHAFLOWERS.COM.      14400   IN      MX      10 aspmx2.googlemail.COM.
SIDDHAFLOWERS.COM.      14400   IN      MX      5
SIDDHAFLOWERS.COM.      14400   IN      MX      5
SIDDHAFLOWERS.COM.      14400   IN      MX      10 aspmx3.googlemail.COM.
SIDDHAFLOWERS.COM.      14400   IN      MX      10
SIDDHAFLOWERS.COM.      14400   IN      MX      10

SIDDHAFLOWERS.COM.      86400   IN      NS      ns2.quickfix8.COM.
SIDDHAFLOWERS.COM.      86400   IN      NS      ns1.quickfix8.COM.

ns1.quickfix8.COM.      14400   IN      A
ns2.quickfix8.COM.      14400   IN      A

;; Query time: 128 msec
;; WHEN: Tue Dec 05 13:08:20 Central Standard Time 2017
;; MSG SIZE  rcvd: 296


The problem is not with the "two" name servers for the domain
you are trying to reach.  Note the quotation marks.
I was able to contact the ONE IP address and get a DNS
response.  If, for some reason, you do not have a path
to that IP address, you will not get a response.  And, there
is no fall-back, as both name servers are on the same IP

--Barry Finkel

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