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

Postfix is a popular, free, and open-source MTA known for its speed, ease of administration, and security features.

Procmail is a Mail Delivery Agent (MDA) or local mail filter, not a full MTA; it processes incoming mail after it has been received by an MTA.

Sendmail is one of the oldest and most well-known MTAs, historically very prevalent in Unix-like systems.

Exim is another powerful and flexible open-source MTA, particularly popular on Linux systems and known for its extensive configuration options.

SMTPd is a generic term often referring to the SMTP daemon (e.g., Postfix's smtpd process) that handles SMTP connections, rather than a specific MTA application name.