In this scenario, ISA Server and Exchange Server are on the same computer, as illustrated below.

You can use the Mail Server Security Wizard to publish the Exchange Server located on the ISA Server computer. In this scenario, the Mail Server Security Wizard creates IP packet filters. IP packet filters are created for each mail service that you select. For example, imagine that you run the Mail Server Security Wizard and specify Outgoing SMTP mail and POP3 client requests.

Outlook/Exchange clients cannot access the Exchange Server from outside the local network using RPC connections. Only POP3 and IMAP4, also supported by Outlook, can be used.
The following IP packet filters are created:

• An IP packet filter allowing Inbound Transmission Control Protocol (TCP) connections on local Port 25 from any remote port (to allow incoming SMTP packets)
• An IP packet filter allowing Outbound TCP connections from all local ports to remote Port 25 (to allow outgoing SMTP packets)
• An IP packet filter allowing Inbound TCP connections on local Port 110 from any remote port (to allow incoming POP3 packets)