EDIT : this might be caused by /etc/postfix/chroot-update scrit missing. I am continuing to investigate.

I wasn't able to have policyd whitelist some domains (by name -> dns), and
looking in the logs, it seemed that the dns resolution was not done by smtpd.
( connect from unknown[ip] / client=unknown(ip) etc...)

Googling around gave me something that seems to work well : copying the
/lib (lib64 in my case) resolv/nss related libs in the postfix chroot (/var/spool/postfix).

Perhaps this is something which is also valid for other distros and that should be
included in the functions/postfix.sh script

==== Required information ====
- iRedMail version: 0.8.5
- Store mail accounts in which backend (LDAP/MySQL/PGSQL): LDAP
- Linux/BSD distribution name and version: Centos 6.x
- Related log if you're reporting an issue:
====