What approach should I take in developing an email-security
strategy?
Because of the danger of viruses, Trojan horses, and spyware and because email
is now the main attack vector, most organizations rely on multiple layers of
defense. Those layers can include a packet-filtering firewall, an email firewall,
and a demilitarized zone (DMZ) mail server.
The first layer of defense—and the layer that best protects the underlying
network and provides a crucial level of protection for network-oriented applications—is
the packet-filtering firewall. A packet-filtering firewall understands networks
at the TCP/IP layer, including such matters as TCP, UDP, and ports. This type
of firewall is configured to let only certain types of incoming packets through
to specifically allowed ports on the internal hosts that the firewall protects.
For example, a firewall might allow incoming packets on TCP port 25 on the DMZ
mail server and TCP port 80 or TCP port 443 on the DMZ Web mail server. . . .
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