help with centos 6.5 iRedmail install

==== Required information ====
- iRedMail version:
- Store mail accounts in which backend (LDAP/MySQL/PGSQL):
- Linux/BSD distribution name and version:
- Related log if you're reporting an issue:
====
I wish to install iRedmail
Server is a base install of centos 6.5
php 5.3.3
no apache yet.
no mysql

since I need mysql 5.5 installed would it be better to use ldap with iRed ?
would that keep iRedmail isolated from touching or installing mysql so I can install mysql 5.5 ?

Also centos comes with postfix preinstalled. Cannot remove postfix as it removes to many other dependencies for the system.
will iRed overwrite postfix properly?

Thanks,
Richard