Which of the following are commonly used Mail Transfer Agent (MTA) applications? (Choose THREE correct answers.)

Postfix is a popular, secure, and easy-to-configure Mail Transfer Agent (MTA) widely used on Unix-like operating systems.

Procmail is a Mail Delivery Agent (MDA), not an MTA. It is used to filter and deliver incoming mail to local mailboxes or other programs.

Sendmail is one of the oldest and most established Mail Transfer Agents (MTAs), historically dominant in the Unix world.

Exim is a flexible and highly configurable Mail Transfer Agent (MTA) popular on Unix-like systems, especially for smaller to medium-sized mail systems.

SMTPd is a generic term often referring to an SMTP daemon (server process), not a specific MTA application name. While MTAs run an SMTP daemon, 'SMTPd' itself is not the name of a common MTA software package.