Skip to main content

Short note: E-mail agents and third functions

Short answer

Email agents include MUA for composing/reading, MTA using SMTP to relay messages, and MAA with POP3/IMAP for retrieval. Together they enable sending, transferring, and accessing email.

Write a short note on E-mail agents and their functions.

E-mail uses several cooperating software agents. Each agent has its own functions: composing and reading, transferring, and delivering/accessing mail.

1. User Agent (UA / MUA) The program used by the person: it composes, edits, reads, replies to, forwards, searches and stores messages, and handles attachments (MIME). Examples: Outlook, Thunderbird, Gmail web.

2. Message Transfer Agent (MTA) Moves messages between mail servers using SMTP (port 25). It queues outgoing mail, looks up the destination with the DNS MX record, retries on failure, and acts as a client when sending and a server when receiving. Examples: Postfix, Sendmail, Exim.

3. Message Access / Delivery Agent (MAA / MDA)

  • The MDA puts the received message into the user's mailbox.
  • The MAA lets the user retrieve mail from the mailbox with POP3 (download and delete), IMAP (manage on the server) or HTTP (web-mail). SMTP is push; POP3/IMAP are pull.
 UA --SMTP--> MTA ==SMTP==> MTA --> MDA --> Mailbox
                                              |
                              UA <--POP3/IMAP-+

Related functions: MIME for non-text content, spam and virus filtering, and aliases or mailing lists.

✓ Answer checked by Claude Opus 5.5 (high effort)

Related questions

All Internet and Intranet chapter 3 questions →