Bind unable to get MX reocrd from Parrent name server

[Fosiul Alam]

Hi
Occasionally we see customer is complainning that we are not able to
resolve mx record when mxtoolbox or other website can resolve their mx
record .
If i do a trace on the domain, i get bellow .

now the problem is :
demeter.is.co.za. and babylon.mitsol.co.za does not know anything
about MX record of that domain. but if i query by using  parent name
server ns1.yithosting.co.za. and ns2.yithosting.co.za , it returns the
mx record .

but mxtoolbox, introdns can resolve the mx record although they
complain the same that

""""
The following nameservers are listed at your nameservers as
nameservers for your domain, but are not listed at the parent
nameservers (see RFC2181 5.4.1). You need to make sure that these
nameservers are working.If they are not working ok, you may have
problems!
demeter.is.co.za
babylon.mitsol.co.za

ERROR: One or more of the nameservers listed at the parent servers are
not listed as NS records at your nameservers. The problem NS records
are:
ns1.yithosting.co.za
ns2.yithosting.co.za
This is listed as an ERROR because there are some cases where nasty
problems can occur (if the TTLs vary from the NS records at the root
servers and the NS records point to your own domain, for example).
""

then why our bind is unable to resolve mx record ???
Thanks for the  help


[root at za-ns-8 ~]# dig  rbcaa.co.za +trace

; <<>> DiG 9.8.2rc1-RedHat-9.8.2-0.17.rc1.el6_4.4 <<>> rbcaa.co.za +trace
;; global options: +cmd
. 447499 IN NS a.root-servers.net.
. 447499 IN NS j.root-servers.net.
. 447499 IN NS l.root-servers.net.
. 447499 IN NS d.root-servers.net.
. 447499 IN NS k.root-servers.net.
. 447499 IN NS g.root-servers.net.
. 447499 IN NS i.root-servers.net.
. 447499 IN NS h.root-servers.net.
. 447499 IN NS m.root-servers.net.
. 447499 IN NS c.root-servers.net.
. 447499 IN NS f.root-servers.net.
. 447499 IN NS e.root-servers.net.
. 447499 IN NS b.root-servers.net.
;; Received 508 bytes from 10.33.91.35#53(10.33.91.35) in 14 ms

za. 172800 IN NS za1.dnsnode.net.
za. 172800 IN NS disa.tenet.ac.za.
za. 172800 IN NS nsza.is.co.za.
za. 172800 IN NS za-ns.anycast.pch.net.
za. 172800 IN NS sns-pb.isc.org.
;; Received 360 bytes from 199.7.83.42#53(199.7.83.42) in 346 ms

co.za. 86400 IN NS ns0.plig.net.
co.za. 86400 IN NS ns.coza.net.za.
co.za. 86400 IN NS ns0.neotel.co.za.
co.za. 86400 IN NS ns1.coza.net.za.
co.za. 86400 IN NS coza1.dnsnode.net.
co.za. 86400 IN NS ns0.is.co.za.
co.za. 86400 IN NS ns4.iafrica.com.
;; Received 266 bytes from 196.4.160.27#53(196.4.160.27) in 285 ms

rbcaa.co.za. 86400 IN NS ns1.yithosting.co.za.
rbcaa.co.za. 86400 IN NS ns2.yithosting.co.za.
;; Received 108 bytes from 196.4.160.17#53(196.4.160.17) in 81 ms

rbcaa.co.za. 14400 IN A 41.203.1.156
rbcaa.co.za. 86400 IN NS demeter.is.co.za.
rbcaa.co.za. 86400 IN NS babylon.mitsol.co.za.
;; Received 99 bytes from 41.203.1.158#53(41.203.1.158) in 41 ms