[CentOS-es] warning: no MX host for thxtransport.com has a valid address record

[Periko Support]

Hola.

Se estan quejando que los correos para un X dominio estan tardando en llegarle.

Revisando los logs para ese correo veo varios warnings/errores en maillog:

Aug 25 09:56:41 mail postfix/smtp[25658]: 8EBC41B006F: to=<XXX>,
relay=none, delay=0.16, delays=0.15/0/0/0, dsn=4.4.3, status=deferred
(Host or domain name not found. Name service error for
name=inbound.registeredsite.com type=A: Host not found, try again)
Aug 25 09:56:41 mail postfix/smtp[25658]: 8EBC41B006F: to=<XXX en XXXX>,
relay=none, delay=0.16, delays=0.15/0/0/0, dsn=4.4.3, status=deferred
(Host or domain name not found. Name service error for
name=inbound.registeredsite.com type=A: Host not found, try again)
Aug 25 10:17:32 mail postfix/cleanup[24175]: BD7EE1B0071:
message-id=<04da01d0df5a$bf9de0b0$3ed9a210$@XXXX>
Aug 25 10:17:32 mail postfix/qmgr[2866]: BD7EE1B0071: from=<XXX en XXXX>,
size=37888, nrcpt=1 (queue active)
Aug 25 10:17:52 mail postfix/smtp[28000]: warning: no MX host for XXXX
has a valid address record
Aug 25 10:17:52 mail postfix/smtp[28000]: 729551B0071: to=<XXXX en XXXX>,
relay=none, delay=10, delays=0.08/0/10/0, dsn=4.4.3, status=deferred
(Host or domain name not found. Name service error for
name=inbound.registeredsite.com type=A: Host not found, try again)
Aug 25 10:18:23 mail postfix/smtp[28000]: warning: no MX host for XXXX
has a valid address record
Aug 25 10:18:23 mail postfix/smtp[28000]: 21B5B1B0073: to=<XXXX en XXXX>,
relay=none, delay=0.05, delays=0.05/0/0/0, dsn=4.4.3, status=deferred
(Host or domain name not found. Name service error for
name=inbound.registeredsite.com type=A: Host not found, try again)
Aug 25 10:26:08 mail postfix/smtp[28578]: warning: no MX host for XXXX
has a valid address record
Aug 25 10:26:08 mail postfix/smtp[28786]: warning: no MX host for XXXX
has a valid address record
Aug 25 10:26:08 mail postfix/smtp[29046]: warning: no MX host for XXXX
has a valid address record

Sera problemas del dns de ellos?

Alguna pista, ya que solo en ese dominio veo estos problemas.

Centos 5.11 x64, gracias!!!