Hi Ravi,
In the BT126H_MAIL cpmponent go to the do_prepare_output method of BT126H_MAIL/send_screen view and default the email body attribute by settign its value by Concatenating its value with "'Sent from SAP CRM'" .
First read the email body attribute value and then concatenate with the alert phrase then Set the attribute with the concatenated value.
Try it once.
Regards,
Rajyalakshmi ch.