After installation, go to Administration → IMSS Configuration → SMTP Routing → Connections and change the listening port of Postfix into 2500.
The following settings are added to the main.cf file during installation:
import_environment = MAIL_CONFIG MAIL_DEBUG 
MAIL_LOGTAG TZ XAUTHORITY DISPLAY LANG=C
LD_PRELOAD=/opt/trend/imss/lib64/libTmFoxSocketLib.so
TM_FOX_PROXY_LIST=/opt/trend/imss/config/foxproxy.list
LD_LIBRARY_PATH=/opt/trend/imss/lib
TM_FOX_PROXY_CONNECT_PORT=2500
Do not remove those settings because they are necessary for the Sender Filtering service to communicate with Postfix.