If the corporate web server has to be read by outsiders, it cannot be hosted on the corporate LAN, as this will often be unreachable. This is not a major issue as it is always a better choice to locate a web server on a highly connected Internet node that is closer to potential viewers. For example, it could be located with a Thai ISP for the Thai public, in Europe for the European public, and so forth. If the Web server is designed both for internal and external users, it can be duplicated on the corporate LAN and on some other web hosting service. This way, confidential insider information is securely separated from public information.
Electronic mail needs specific consideration.
Corporate users want to receive email at an address of the form . Every email that is received by the gateway will either be delivered to a mailbox if it is addressed to a local user, or else sent to the next email gateway. ETRN allows one gateway to actively request all incoming email instead of passively waiting for it. Email sending between gateways is thus initiated by the receiving end instead of the sending end. The ISP can be nominated as the email gateway for all corporate incoming email, which then awaits an ETRN request from the corporate gateway.