I got the content of the link.
To explain you well my target/goal please see below scenario:
Here is my scenario:
1. Running Postfix/dovecot in site 1
2. Site 1 and site 2 Connection running in VPN Tunnel.
Receive Email from other domain, setup as MX record, POP3 Server of local user(site1) and Site2 users.
1. Setup postfix/Dovecot server in site 2 that pull email from Site1 POP3 Server (POP3 Download).
2. Users in Site2 only check mail in local server, to avoid multiple connection in tunnel.