query regarding memory where the mails are stored

[darshan]

i know that it is stored on zimbra server but where is the code for storing the mails and in which directories they are stored because i want to devlop a new module for blocking the mail which is from sender who is not in receveirs address book now u understand my quetion?
so plz help me in that so i can know in which files i required to make change
thank you