D-Link DFL-600 - Manual (Page 42)

POP3 The Post Office Protocol, version 3. This is used
to view and retrieve e-mail from a POP3 server
on the WAN.
Server IP Enter the IP address of your POP3 server here.
Your ISP should provide you with this address.
Server Port This is the TCP port number that the POP3
server will use to communicate with PCs on your
LAN. TCP port 110 is the ‘well known’ or
default port used for the POP3 protocol.
RADIUS
The Remote Access Dial-in User Service (RADIUS) is one of the most
common protocols used to carry authorization, authentication, and
configuration information between a RADIUS server on the WAN and PCs
on your LAN. Choosing RADIUS will allow the DFL-600 to connect PCs on
your LAN to a RADIUS server on the WAN. If RADIUS user authentication
is enabled on the DFL-600, PCs on your LAN will require entering a
Username and Password into the Windows Logon dialog box before they can
access the Internet.