I have another mailserver on a different location. I want that all the users of a certain domain use an external mailserver at an other location. How can i do this within ISPConfig? I know it is possible to select the option "Extern Mailserver" in the ISP-site module within ISPConfig. But i do not understand how this works.. Is it not necessary to specifify an new IP-address of the External mailserver? Please let me know.