Modify email recipient for PO

Hi everybody,

In SRM, when a PO is ordered, an email is sent to the supplier address.

The standard method "PROCESS_BBP_PO_MAI"  of the class "CL_PD_PO_PROCESSING_BBP" is executed and the smartform is sent by email.

The import parameter "IS_MAIL_RECIPIENT" contains the information about the supplier email because the Funcion Module "GET_RECIPIENT_DATA_PPF" is called at the middle of the code with this variable returning the supplier email.

In our PO header, we have a custom field with the email recipient. How can I change the mail recipient so it takes the custom one?