Detail
Some ISPs will try to send messages to you via SMTP, rather than assume you are going to collect them via POP3, if they see an SMTP server running on your IP address.
To ensure that the ISP does not push e-mail to you via SMTP, do the following:
In the Interfaces page of the Settings property sheet of the Administrator program, set the SMTP interface to be the IP address of the local network card for the server machine, rather than [All Interfaces]. This prevents the ISP from detecting the presence of an SMTP server on the connecting interface and subsequently trying to push mail to you.
This will only work if the computers local IP address is different from it’s Internet IP address, for example, if you dial-up to connect to the Internet, or if the computer is multi-homed (I.e. has 2 network cards). If you have a permanent connection to the Internet and your computer only has one IP address, then you should either consider purchasing another network card so that you can have a separate local interface, or you should consider receiving your e-mail via SMTP rather than POP3.
Note, not all ISPs push mail to you via SMTP as described above. This answer specifically refers to Demon ISP in the United Kingdom but could apply to other ISPs.