450 4.1.2 Recipient address rejected: Domain not found;

==== Required information ====
- iRedMail version: 0.7.2
- Store mail accounts in which backend (LDAP/MySQL/PGSQL): Mysql
- Linux/BSD distribution name and version: Centos 5.4 64 Bit
- Related log if you're reporting an issue: 450 4.1.2 <XXXi@XXX.com>: Recipient address rejected: Domain
not found; from=<yyy@yyy.com> to=<xxx@xxx.com> proto=ESMTP helo=<[127.0.0.1]>
====

Hi am using IRedMail with Centos . receiving below error for some times. Please help to resolve
450 4.1.2 <XXXi@XXX.com>: Recipient address rejected: Domain
not found; from=<yyy@yyy.com> to=<xxx@xxx.com> proto=ESMTP helo=<[127.0.0.1]>

my Nameservers entry is same in both /etc/resolve.conf and /var/spool//postfix/etc/resolve.conf

Please suggest.

Thanks and regards,
Nishad Virkud