Mail servers are available in almost any organization because e-mail has taken over as the preferred communication channel for obvious reasons. The importance of mail servers depends on the information stored in them. Attackers often compromise an e-mail account and proceed to take over all other accounts found by using the "Forgot password" functionality available in almost every web application. Sometimes compromised accounts are simply eavesdropped for months without anyone noticing, and may even be abused by spammers. Therefore, any good system administrator knows it is essential to have a secure mail server.
In this chapter I will go through different NSE tasks for administering and monitoring mail servers. I will also show the offensive side available to penetration testers. We will cover the most popular mail protocols such as SMTP, POP3, and IMAP.
We will review tasks such as retrieving capabilities, enumerating users, brute forcing passwords, and even exploiting vulnerable...