sometimes my zimbra server down. This could be a memory problem??, because the top command said I have enough space there.

[zimbra@host ~]$ zmcontrol status
Host host.domain.com
antispam Running
antivirus Running
ldap Running
logger Running
mailbox Stopped
zmmailboxdctl is not running.
mta Running
snmp Running
spell Running
stats Running
zmconfigd Running

thanks in advance