All of the following are Mail Transport Agents EXCEPT:

Exim is a widely used open-source Mail Transfer Agent (MTA) for Unix-like operating systems.

Postfix is a free and open-source Mail Transfer Agent (MTA) that routes and delivers electronic mail.

Sendmail is one of the oldest and most well-known Mail Transfer Agents (MTAs) for Unix-like systems.

qmail is a secure, reliable, and efficient Mail Transfer Agent (MTA) designed to replace Sendmail.

mail (or mailx) is typically a Mail User Agent (MUA) or a command-line utility used to send and receive mail, interacting with an MTA, but it is not an MTA itself. Mail Transport Agents are responsible for transferring email between mail servers.