15.1 About Email Programs

A Mail User Agent is an email client application that allows you to create and read email messages, set up mailboxes to store and organize messages, and send outbound messages to a Mail Transfer Agent (MTA). Many MUAs can also retrieve email messages from remote servers using the Post Office Protocol (POP) or Internet Message Access Protocol (IMAP).

A Mail Transfer Agent (MTA) transports email messages between systems by using the Simple Mail Transport Protocol (SMTP). The mail delivery services from the client program to a destination server possibly traverses several MTAs in its route. Oracle Linux offers two MTAs, Postfix and Sendmail, and also includes the special purpose MTA, Fetchmail for use with SLIP and PPP.

A Mail Delivery Agent (MDA) performs the actual delivery of an email message. The MTA invokes an MDA, such as Procmail, to place incoming email in the recipient’s mailbox file. MDAs distribute and sort messages on the local system that email client application can access.