I have only 1 domain and 1 external IP address, which is pointed to 1 apache server, in the same network there is my mail server which is working fine, and DO have a webmail, webmail is accessible only to user on the intranet, i created a subdomain webmail.ourcompany.com and pointed to the same apache server, i want apache to forward all requisitions to webmail.ourcompany.com to the local server 192.168.5.23. i am pretty sure apache can do this, just dont know how...
Use something known as ProxyPass through the Apache config file, I believe it should lead you in the correct direction. Since it is an internal IP (192.x.x.x), you need to have a proxy that sits on the local network to relay the traffic since the data is only accessible on the internal network.