I would recommend against exposing yourself the way you are. Instead you should use ssh port forwarding (or VPN).
Here is an example of how you would use ssh port forwarding from a Linux machine outside your office.
sshServer - server running ssh
XXX - port ssh on sshServer is exposed on
zimbraServer - server running zimbra
execute:
ssh -p XXX -l username -L 7071:zimbraServer:7071 sshServer cat -
Then go to:
https://localhost:7071 in your web browser