zmmailboxdctl is not running.

[Heatryn]

One in a while, my server crashes and when I do zmcontrol status, I get:

zimbra@jupiter:~$ zmcontrol status
Host jupiter.joelcraenhals.be
	antispam                Running
	ldap                    Running
	logger                  Running
	mailbox                 Stopped
		zmmailboxdctl is not running.
	mta                     Running
	spell                   Running
	zmconfigd               Running

Here is the log:

zimbra@jupiter:~$ tail /var/log/zimbra.log 
Jun 21 20:03:15 jupiter zmmailboxdmgr[21921]: no manager process is running
Jun 21 20:03:15 jupiter zmmailboxdmgr[21930]: status requested
Jun 21 20:03:15 jupiter zmmailboxdmgr[21930]: stale pid 21081 found in /opt/zimbra/log/zmmailboxd_manager.pid: No such process
Jun 21 20:03:15 jupiter zmmailboxdmgr[21930]: assuming no other instance is running
Jun 21 20:03:15 jupiter zmmailboxdmgr[21930]: file /opt/zimbra/log/zmmailboxd.pid does not exist
Jun 21 20:03:15 jupiter zmmailboxdmgr[21930]: assuming no other instance is running
Jun 21 20:03:15 jupiter zmmailboxdmgr[21930]: no manager process is running
Jun 21 20:03:29 jupiter postfix/anvil[20270]: statistics: max connection rate 1/60s for (smtp:195.130.132.48) at Jun 21 19:59:06
Jun 21 20:03:29 jupiter postfix/anvil[20270]: statistics: max connection count 1 for (smtp:195.130.132.48) at Jun 21 19:59:06
Jun 21 20:03:29 jupiter postfix/anvil[20270]: statistics: max cache size 1 at Jun 21 19:59:06

How can this be resolved?