Zimbra (mailbox) stops working

[agd]

Hi,

I installed a few days ago Zimbra (5.0.6_GA_2313.RHEL5_20080522104341 CentOS5 FOSS edition).
Everything seems to works fine, but almost 2 or 3 days the mailbox service stops working:

[zimbra@srv ~]$ zmcontrol status
Host mail.xxxxx.com
ldap Running
logger Running
mailbox Stopped
zmmailboxdctl is not running
mta Running
snmp Running
spell Running
stats Running


I checked the DNS service, hardware, and everything seems to be working fine. What can I do?

Thanks in advance.
Regards,
AGD

p.d.
Sorry about my English, is not my native language.