CC Proxy can work as mail proxy server for Outlook Express for Gmail.

CCProxy is an easy-to-use proxy server software. Full supports Windows 98/ME/NT/2000/XP. For more details of CCProxy, please click here. Also you can download it here for a trial.

CCProxy-> "Options" -> "Port Map", click the "E" button and add two port map rules:
1) Dest Host: smtp.gmail.com, Dest Port: 465, Type: TCP, Local Port: 465.
2) Dest Host: pop.gmail.com, Dest Port: 995, Type: TCP, Local Port: 995.

In Outlook Express account property, set smtp and pop3 server address as the proxy address (i.e. 192.168.0.1).