autogenerated email in va02 as per user login

hi experts,

i have a senario where user wise can change the delivery date in va02,

when any user changes delivery date in va02 then immediately mail should be generated and send this mail to higher level authorization.

which include is used to write the mail code after click on save button.

i tried this

USEREXIT_SAVE_DOCUMENT.

USEREXIT_SAVE_DOCUMENT_PREPARE

but not working

plz help me

Thanks