Which of the following are commonly used Mail Tranfer Agent (MTA) applications?

(Please select THREE correct answers)

A.
postfix

B.
procmail

C.
sendmail

D.
exim

E.
smtpd

Explanation/Reference:
smtpd is a mail proxy for firewalls with anti-spam and anti-relay features Smtpd uses two programs, smtpd which listens for incoming mail and places it in a private queue, and smtpfwdd, which invokes sendmail to deliver messages from the queue.
procmail is a mail delivery agent (MDA) capable of sorting incoming mail into various directories and filtering out spam messages. Procmail is widely used on Unix-based systems and stable, but no longer maintained; users who wish a maintained program are advised to use an alternative MDA, such as maildrop.