D@emon,
Does this project looks like "teach me server and Linux administration"? Do you know how to set valid email box with DNS,DKIM settings and tld domain names? Do you know that mass mailing is illegal? Do i need to say more?
If you want to clear you up and learn something useful, maybe you need to start to ask right questions. Now, because I'm nice dude i will give you some directions.
1. First project for you will be to learn how to set email server for local network, not Internet users. When you do that you will get some answers on your question, but not all. Then you will learn about SMTP and POP or IMAP services or how mail goes out or comes in your mail box.
2. You need to learn how to use command find. This command will save a lot of your time searching for config files, like find / -name setoolkit
3. You need to learn, if not to code, to understand code you want/need to edit.
And here we go, you can play with mass mail in local with setoolkit. Most of devs stopped working of mass mailers for pen testers because of people who want to abuse. My final message is "DON'T BE ONE OF THEM", do something good.
