Sounds like your router is probably doing NAT for the outbound traffic, but it needs also to do DNAT (Destination Network Address Translation) for the inbound traffic. The usual way this is done is to have a second public IP address as an alternate address on the WAN port of your router, and then program the router to accept port 25, port 443, and others if desired) and route all such traffic to the internal address of your Zimbra box 192.168.1.110. Right now, if you try to access the router's WAN address, it responds "gee, I don't have an https server on me" and rejects or drops the traffic.
Cheers,
Dan |