So are you saying that the build in alert does not work for you? How do you test it?
Or are you just trying to get an email alert for this build in alert? If yes, I use the following for my transmit alert. But I've left the build in one as it is and have just written another alert that just sends the email. I have set it to only alert me if it's transmitting over 90% continuously for 10 mins.
Interface <b>${Caption}</b> on node <b>${NodeName}</b> transmitted at <b>${Interface.OutPercentUtil}%</b> of its utilization, which triggered this alert.