MS Enviorment parameters - customizing BPF email subject

Hi

In the environment parameters I have updated the BPF email content - BPFAFTER_NOTIFY_MSG which sets the body of the email. However I also want to be able to customize the subject line. I assume the parameter will be something like BPFAFTER_NOTIFY_SUBJECT but this doesn't work.

Do you know firstly if I can customize the subject like and secondly what the parameter is?

Thanks