Hi Oykun,
You can assign multiple Virtual IP addresses to an interface and configure Inbound and Outbound mail IP addresses using those virtual IPs. Please see the sections titled "Configuring Ethernet settings", "About configuring inbound SMTP Scanner settings", and "About configuring outbound SMTP Scanner settings" in the Symantec Brightmail Gateway 8.0 Administration Guide available here:
ftp://ftp.entsupport.symantec.com/pub/support/documentation/sbg_administration_guide.pdf
You may also want to choose which IP addresses are used by the scanner to deliver mail. This is achieved using the SMTP Delivery Bindings settings For details, please see the section titled "Message delivery phase processing details" in the Admin Guide.
Regards,
Adnan