E-Mail user in sql

Hello,
I have desactivate private message in user accompte.
After i view a listing and clic on “contact author” and send an e-mail.

I received my mail ok !

I return in the admin panel and reactivate the option private message, and my mail is save in my account…… Why ?
If i desactivate this option why are she save in the sql ? after one or two year if the user don’t delete the message my sql will be bigguest ?
Have a solution for desactivate save mail if option is desactivate ?
Or where the code for delete?

Thank’s and sorry for my english