If you need port 8443, from what I read on Speedguide it is used by any of these services:
PCsync HTTPS, PCSync SSL, Common alternative https port, SW Soft Plesk Control Panel, Apache Tomcat SSL, iCal service (SSL) SG
8443 tcp SW Soft Plesk Control Panel (unofficial) Wikipedia
8443 tcp,udp pcsync-https PCsync HTTPS IANA
8443 tcp pcsync-ssl PCSync SSL SANS
8443 tcp https-alt Common alternative https port
If you are not using the transparent proxy, then you would have to allow this port in Squid's config file, it will be somewhere in this line:
acl SSL_ports port 443 563 # https, snews
change to
acl SSL_ports port 443 563 8443 # https, snews
You have to hack into the .mas file that is here in Zentyal 2.2.7:
/usr/share/zentyal/stubs/squid
You can perhaps add por 8444 also. After the change, restart proxy service and you are good to go.
Cheers.