Traffic to the Z39.50 port on the proxy server is simply passed directly to the primary server by the FastForward program. This program can be used to forward many types of services from one machine to another if no processing on the proxy system is required. In this case the program is forwarding connections to port 5555 on the proxy server to an Isite program running on the primary server. Incoming e-mail is received by the proxy machine using the sendmail replacement program named postfix. The postfix program offers improved security over sendmail in that it does not run as root for most of its functions.
Postfix uses text based configuration files which are easy to read and reconfigure.
The postfix program on the proxy redirects the incoming e-mail to the primary development system. By using the 'masquerade as' function, the mailer on the development system changes the local addresses on outgoing mail so that replies are sent back to the proxy system. The presence of the proxy server allows for improved availability of the proxied services to clients. The primary server can be taken down for maintenance, and the proxy will automatically switch to the backup server. If the proxy server itself requires maintenance, a second proxy system is available to be swapped into the network with only a few minutes down time.