Be careful your script does not get labeled as spam or they could suspend your reseller account all together. You should probably let them know what you intend on doing. Hiding things from your provider does not make them happy if it causes a high server load or slows other clients emails down. If you contact them and they say yes and then there is an issue they have a place to start looking. php based mailer scripts are hard to track down sometimes if it starts causing issues. All they do is frustrate your provider. Knowing is half the battle.

You could get suspended or terminated based on your actions.