Multiple Webservers behind single IP

Hey, We are trying to route multiple exchanges (separate domains/clients) behind a limited IP pool within our Fortiweb

This will be for OWA/Activesync access only.

However, the GUI is erroring when I try to publish multiple endpoints within the same virtual server unless I use bespoke ports (which makes activesync problematic). All sites will be different hostnames and different destination server but the same protocol (https)

eg. domain1.com.au and domain2.com.au pointing to 10.10.10.10 but. routing to 9.9.9.9 and 8.8.8.8 respectively (names and IP's for placeholders only)

Thanks in advance