pop3 proxy configuration

hai,

i am confused every time with pop3 proxy configuration... and this is the first time i am going to try, so any one can provide me complete resource to understand how pop3 proxy works...

my scenario is i have exchange 2007 in my network and ASG 220

i configured SMTP for local users ....
mail security-->smtp--> go to tab
global----- simple mode
routing ---
domains (example.com)
route by (static host list)
host list (local exchange server)

relaying
host based relay --- allowed hosts/networks -(local exchange server)

by the above configuration (without smarthost) SMTP work fine.

now i have some mobile users who move outside company to different places so now i want to make pop3 so that they get mail in their outlook using pop3.

now with the same scenario what i need to do to configure pop3 proxy in astaro...

please correct me if my SMTP proxy settings are wrong ?

i am not new to astaro but for mail security i need to work around so please help me with your ideas...

thanks in advance