F-SECURE ANTI-VIRUS FOR MICROSOFT EXCHANGE 7.10 Administrator's Manual page 225

if they are sent from the internal SMTP sender host.
If e-mail messages come from internal SMTP sender hosts and
contain both internal and external recipients, messages are split
and processed as internal and outbound respectively.
Internal Domains Specify internal domains. All messages coming
to internal domains are considered to be
inbound mail.
Separate each domain name with a space. You
can use an asterisk (*) as a wildcard. For
example, *example.com internal.example.net
Internal SMTP Specify the IP addresses of hosts that belong to
senders your organization. Specify all hosts within the
organization that send messages to Exchange
Edge or Hub servers via SMTP as Internal
SMTP Senders.
Separate each IP address with a space. An IP
address range can be defined as:
You can use an asterisk (*) to match any number
or dash (-) to define a range of numbers. For
example,
172.16.4.4 172.16.*.1 172.16.4.0-16
172.16.250-255.*
Administration with Web Console
a network/netmask pair (for example,
10.1.0.0/255.255.0.0), or
a network/nnn CIDR specification (for
example, 10.1.0.0/16).
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