Zimbra reports “ Error: Queue report unavailable – mail system is down ”

zcs @ zimbra: ~ $ zmcontrol status
Host zcs.ilba.cat
        antispam                Running
        antivirus               Running
        convertd                Running
        ldap                    Running
        LOGGER Running
        mailbox                 Running
        mta                     Running
        opendkim                Running
        proxy                   Running
        snmp                    Running
        spell                   Running
        stats                   Running
        zmconfigd               Running

zimbra@zcs:~$ tail -f /var/log/mail.log
Jan 22 11:08:00 zcs postfix/postqueue[19195]: fatal: Queue report unavailable - mail system is down

root@zcs:~# locate master.pid
/opt/zimbra/data/postfix/spool/pid/master.pid

zcs root @: ~ # mv master.pid master.pid.bak.21des2016

root@zcs:~# su - zimbra

Zimbra ZCS @: ~ $ / opt / Zimbra / bin / zmmtactl start
Rewriting configuration files...done.
Starting saslauthd...already running.
/postfix-script: starting the Postfix mail system