Which of the following is NOT a Mail Transport Agent?
A.
exim

B.
postfix

C.
sendmail

D.
qmail

E.
mail

Explanation/Reference:
From wikipedia:
postfix is a free and open-source mail transfer agent (MTA) that routes and delivers electronic mail. It is intended as a fast, easier-to-administer, and secure alternative to the widely-used sendmail MTA.
sendmail is the […] standard MTA under most variants of the Unix.
exim is a message transfer agent (MTA) developed at the University of Cambridge for use on Unix systems.
qmail is a mail transfer agent (MTA) that runs on Unix. It was written, […] as a more secure replacement for the popular sendmail program.

mail is a command line e-mail client to send/create mails.