When it comes to email, what is Postfix?

When it comes to email, what is Postfix?

• A mail user agent
• Paid software
• A mail submission agent
• A mail transfer agent 

 

EXPLANATION

Postfix is a mail transfer agent (MTA), which handle the long-haul delivery of the mail to other MTAs. Postfix supports LDAP, SMTP AUTH (SASL), TLS, and running in a chroot environment.