Mail server stop delivering and receiving

==== Required information ====
- iRedMail version: 0.8.5
- Store mail accounts in which backend (LDAP/MySQL/PGSQL): MySQL
- Linux/BSD distribution name and version: Centos 6.4
- Related log if you're reporting an issue: nil
====

Hi everyone. After installing iRedmail, I keep encountering the need of rebooting the server every hour or two, so that it will not stop delivering and receiving. I am still able to access the iRedmail Admin and Roundcube all the time. Do I have to reboot the server all the time?

Thanks.