Postfix check to see if e-mail is correct

Hiya.

I am having issues with some customers having their e-mail password stolen, so spammers can log in and send e-mail. That is easy to fix, but to dam up for the damages, is it possible to get postfix to check if from e-mail exist in the database?

Example:
Spammer logs in to [email protected] and sends e-mails from [email protected] and [email protected], where aa and ab doesn't exist.