If you will get a prompt stating something like “Port conflict detected: 53 (zimbra-dnscache)” with a prompt to hit ENTER to continue, you can just hit enter and let the installation/upgrade run out. Once everything is running, you will see that the Zimbra DnsCahe service is in a stopped state. To fix this error, all you have to do is

# zmcontrol status
# zmprov ms `zmhostname` -zimbraServiceEnabled dnscache
# zmprov ms `zmhostname` -zimbraServiceInstalled dnscache
# zmcontrol status

You will see that the service is removed from Zimbra’s Services.

[zimbra@mail root]$ zmcontrol status
Host mail.server.lan
amavis Running
antispam Running
antivirus Running
ldap Running
logger Running
mailbox Running
memcached Running
mta Running
opendkim Running
proxy Running
service webapp Running
snmp Running
spell Running
stats Running
zimbra webapp Running
zimbraAdmin webapp Running
zimlet webapp Running
zmconfigd Running