See my zimbra.log of this night. I had to reboot it manually with zmcontrol start.

Code:
Nov 30 01:30:06 localhost zmtomcatmgr[12822]: status requested
Nov 30 01:30:06 localhost zmtomcatmgr[12822]: status OK
Nov 30 01:30:06 localhost zimbramon[12719]: 12719:info: 2006-11-30 01:30:02, STATUS: mydomain.com: ldap: Running
Nov 30 01:30:06 localhost zimbramon[12719]: 12719:info: 2006-11-30 01:30:02, STATUS: mydomain.com: logger: Running
Nov 30 01:30:06 localhost zimbramon[12719]: 12719:info: 2006-11-30 01:30:02, STATUS: mydomain.com: mailbox: Running
Nov 30 01:30:06 localhost zimbramon[12719]: 12719:info: 2006-11-30 01:30:02, STATUS: mydomain.com: mta: Running
Nov 30 01:30:06 localhost zimbramon[12719]: 12719:info: 2006-11-30 01:30:02, STATUS: mydomain.com: snmp: Running
Nov 30 01:30:06 localhost zimbramon[12719]: 12719:info: 2006-11-30 01:30:02, STATUS: mydomain.com: spell: Running
Nov 30 01:32:01 localhost postfix/postfix-script: stopping the Postfix mail system
Nov 30 01:32:01 localhost postfix/master[21319]: terminating on signal 15
Nov 30 01:32:02 localhost zmtomcatmgr[13022]: threaddump requested
Nov 30 01:32:02 localhost zmtomcatmgr[9508]: sending SIQUIT to tomcat/JVM process 9509
Nov 30 01:32:04 localhost zmtomcatmgr[13038]: stop requested
Nov 30 01:32:04 localhost zmtomcatmgr[9508]: shutdown requested, sending TERM signal to 9509
Nov 30 01:32:04 localhost zmtomcatmgr[13038]: waiting for manager process 9508 to die
Nov 30 01:32:04 localhost zmtomcatmgr[13062]: status requested
Nov 30 01:32:04 localhost zmtomcatmgr[13062]: status OK
Nov 30 01:32:04 localhost postfix/postqueue[13072]: fatal: Queue report unavailable - mail system is down
Nov 30 01:32:05 localhost zimbramon[12970]: 12970:info: 2006-11-30 01:32:01, STATUS: mydomain.com: ldap: Running
Nov 30 01:32:05 localhost zimbramon[12970]: 12970:info: 2006-11-30 01:32:01, STATUS: mydomain.com: logger: Running
Nov 30 01:32:05 localhost zimbramon[12970]: 12970:info: 2006-11-30 01:32:01, STATUS: mydomain.com: mailbox: Running
Nov 30 01:32:05 localhost zimbramon[12970]: 12970:info: 2006-11-30 01:32:01, STATUS: mydomain.com: mta: Stopped
Nov 30 01:32:05 localhost zimbramon[12970]: 12970:info: 2006-11-30 01:32:01, STATUS: mydomain.com: snmp: Running
Nov 30 01:32:05 localhost zimbramon[12970]: 12970:info: 2006-11-30 01:32:01, STATUS: mydomain.com: spell: Running
Nov 30 01:32:07 localhost zmtomcatmgr[9508]: tomcat/JVM process exited (waitpid expected 9509 got 9509)
Nov 30 01:32:07 localhost zmtomcatmgr[9508]: manager woke up from wait on tomcat/JVM with pid 9509
Nov 30 01:32:07 localhost zmtomcatmgr[13038]: manager process 9508 died, shutdown completed
Nov 30 01:33:14 localhost postfix/postqueue[13155]: fatal: Queue report unavailable - mail system is down
Nov 30 01:33:16 localhost postfix/postfix-script: warning: not owned by root: /opt/zimbra/postfix-2.2.9/conf/main.cf
Nov 30 01:33:16 localhost postfix/postfix-script: starting the Postfix mail system
Nov 30 01:33:16 localhost postfix/master[13203]: daemon started -- version 2.2.9, configuration /opt/zimbra/postfix-2.2.9/conf
Nov 30 01:33:16 localhost zmtomcatmgr[13225]: threaddump requested
Nov 30 01:33:16 localhost zmtomcatmgr[13225]: file /opt/zimbra/log/zmtomcatmgr.pid does not exist
Nov 30 01:33:16 localhost zmtomcatmgr[13225]: assuming no other instance is running
Nov 30 01:33:16 localhost zmtomcatmgr[13225]: no manager process is running
Nov 30 01:33:18 localhost zmtomcatmgr[13232]: stop requested
Nov 30 01:33:18 localhost zmtomcatmgr[13232]: file /opt/zimbra/log/zmtomcatmgr.pid does not exist
Nov 30 01:33:18 localhost zmtomcatmgr[13232]: assuming no other instance is running
Nov 30 01:33:18 localhost zmtomcatmgr[13232]: no manager process is running
Nov 30 01:34:04 localhost zmtomcatmgr[13293]: status requested
Nov 30 01:34:04 localhost zmtomcatmgr[13293]: file /opt/zimbra/log/zmtomcatmgr.pid does not exist
Nov 30 01:34:04 localhost zmtomcatmgr[13293]: assuming no other instance is running
Nov 30 01:34:04 localhost zmtomcatmgr[13293]: no manager process is running
Nov 30 01:34:04 localhost zimbramon[13234]: 13234:info: 2006-11-30 01:34:02, STATUS: mydomain.com: ldap: Running
Nov 30 01:34:04 localhost zimbramon[13234]: 13234:info: 2006-11-30 01:34:02, STATUS: mydomain.com: logger: Running
Nov 30 01:34:04 localhost zimbramon[13234]: 13234:info: 2006-11-30 01:34:02, STATUS: mydomain.com: mailbox: Stopped
Nov 30 01:34:04 localhost zimbramon[13234]: 13234:info: 2006-11-30 01:34:02, STATUS: mydomain.com: mta: Stopped
Nov 30 01:34:04 localhost zimbramon[13234]: 13234:info: 2006-11-30 01:34:02, STATUS: mydomain.com: snmp: Running
Nov 30 01:34:04 localhost zimbramon[13234]: 13234:info: 2006-11-30 01:34:02, STATUS: mydomain.com: spell: Running
And the yesterday night:

Code:
Nov 29 05:02:04 localhost zimbramon[21009]: 21009:info: 2006-11-29 05:02:01, STATUS: grass.intra.comune.trento.it: ldap: Running
Nov 29 05:02:04 localhost zimbramon[21009]: 21009:info: 2006-11-29 05:02:01, STATUS: grass.intra.comune.trento.it: logger: Running
Nov 29 05:02:04 localhost zimbramon[21009]: 21009:info: 2006-11-29 05:02:01, STATUS: grass.intra.comune.trento.it: mailbox: Running
Nov 29 05:02:04 localhost zimbramon[21009]: 21009:info: 2006-11-29 05:02:01, STATUS: grass.intra.comune.trento.it: mta: Running
Nov 29 05:02:04 localhost zimbramon[21009]: 21009:info: 2006-11-29 05:02:01, STATUS: grass.intra.comune.trento.it: snmp: Running
Nov 29 05:02:04 localhost zimbramon[21009]: 21009:info: 2006-11-29 05:02:01, STATUS: grass.intra.comune.trento.it: spell: Running
Nov 29 05:02:30 localhost postfix/smtpd[21096]: connect from servertwo.intra.comune.trento.it[192.168.8.4]
Nov 29 05:02:30 localhost postfix/trivial-rewrite[21099]: warning: do not list domain grass.intra.comune.trento.it in BOTH mydestination and virtual_mailbox_
domains
Nov 29 05:02:30 localhost postfix/smtpd[21096]: F0A662F32F: client=servertwo.intra.comune.trento.it[192.168.8.4]
Nov 29 05:02:31 localhost postfix/cleanup[21100]: F0A662F32F: message-id=<20061128232046.38A951368C9F@mail.hwmail.it>
Nov 29 05:02:31 localhost postfix/qmgr[15947]: F0A662F32F: from=<newsletter@hwmail.it>, size=21379, nrcpt=1 (queue active)
Nov 29 05:02:31 localhost postfix/smtpd[21096]: disconnect from servertwo.intra.comune.trento.it[192.168.8.4]
Nov 29 05:02:31 localhost postfix/trivial-rewrite[21099]: warning: do not list domain grass.intra.comune.trento.it in BOTH mydestination and virtual_mailbox_
domains
Nov 29 05:02:31 localhost postfix/lmtp[21102]: F0A662F32F: to=<fioronig@grass.intra.comune.trento.it>, relay=grass.intra.comune.trento.it[192.168.13.51], del
ay=1, status=sent (250 2.1.5 OK)
Nov 29 05:02:31 localhost postfix/qmgr[15947]: F0A662F32F: removed
Nov 29 05:02:39 localhost postfix/postfix-script: stopping the Postfix mail system
Nov 29 05:02:39 localhost postfix/master[6012]: terminating on signal 15
Nov 29 05:02:39 localhost zmtomcatmgr[21193]: threaddump requested
Nov 29 05:02:39 localhost zmtomcatmgr[5807]: sending SIQUIT to tomcat/JVM process 4126
Nov 29 05:02:41 localhost zmtomcatmgr[21200]: stop requested
Nov 29 05:02:41 localhost zmtomcatmgr[21200]: waiting for manager process 5807 to die
Nov 29 05:02:41 localhost zmtomcatmgr[5807]: shutdown requested, sending TERM signal to 4126
Nov 29 05:02:44 localhost zmtomcatmgr[5807]: tomcat/JVM process exited (waitpid expected 4126 got 4126)
Nov 29 05:02:44 localhost zmtomcatmgr[5807]: manager woke up from wait on tomcat/JVM with pid 4126
Nov 29 05:02:45 localhost zmtomcatmgr[21200]: manager process 5807 died, shutdown completed
Nov 29 05:03:52 localhost postfix/postqueue[21271]: fatal: Queue report unavailable - mail system is down
Nov 29 05:03:54 localhost postfix/postfix-script: warning: not owned by root: /opt/zimbra/postfix-2.2.9/conf/main.cf
Nov 29 05:03:54 localhost postfix/postfix-script: starting the Postfix mail system
Nov 29 05:03:54 localhost postfix/master[21319]: daemon started -- version 2.2.9, configuration /opt/zimbra/postfix-2.2.9/conf
Nov 29 05:03:54 localhost zmtomcatmgr[21341]: threaddump requested
Nov 29 05:03:54 localhost zmtomcatmgr[21341]: file /opt/zimbra/log/zmtomcatmgr.pid does not exist
Nov 29 05:03:54 localhost zmtomcatmgr[21341]: assuming no other instance is running
Nov 29 05:03:54 localhost zmtomcatmgr[21341]: no manager process is running
Nov 29 05:03:56 localhost zmtomcatmgr[21348]: stop requested
Nov 29 05:03:56 localhost zmtomcatmgr[21348]: file /opt/zimbra/log/zmtomcatmgr.pid does not exist
Nov 29 05:03:56 localhost zmtomcatmgr[21348]: assuming no other instance is running
Nov 29 05:03:56 localhost zmtomcatmgr[21348]: no manager process is running
Nov 29 05:04:04 localhost zmtomcatmgr[21409]: status requested
Nov 29 05:04:04 localhost zmtomcatmgr[21409]: file /opt/zimbra/log/zmtomcatmgr.pid does not exist
Nov 29 05:04:04 localhost zmtomcatmgr[21409]: assuming no other instance is running
Nov 29 05:04:04 localhost zmtomcatmgr[21409]: no manager process is running
Nov 29 05:04:04 localhost zimbramon[21350]: 21350:info: 2006-11-29 05:04:01, STATUS: grass.intra.comune.trento.it: ldap: Running
Nov 29 05:04:04 localhost zimbramon[21350]: 21350:info: 2006-11-29 05:04:01, STATUS: grass.intra.comune.trento.it: logger: Running
Nov 29 05:04:04 localhost zimbramon[21350]: 21350:info: 2006-11-29 05:04:01, STATUS: grass.intra.comune.trento.it: mailbox: Stopped
Nov 29 05:04:04 localhost zimbramon[21350]: 21350:info: 2006-11-29 05:04:01, STATUS: grass.intra.comune.trento.it: mta: Stopped
Nov 29 05:04:04 localhost zimbramon[21350]: 21350:info: 2006-11-29 05:04:01, STATUS: grass.intra.comune.trento.it: snmp: Running
Nov 29 05:04:04 localhost zimbramon[21350]: 21350:info: 2006-11-29 05:04:01, STATUS: grass.intra.comune.trento.it: spell: Running

A question: why Zimbra doesn't automatically boot a service if it is down?