Which of the following is true about a message transfer agent (MTA)?
- Forwards incoming email to the right destination
- Uses peer-to-peer application architecture
- Implements only the server portion of SMTP
- Implements only the client portion of SMTP
EXPLANATION
Message transfer agent within
Internet message handling services, a message transfer agent or mail
transfer agent or mail relay is software that transfers electronic mail
messages from one computer to another using a client–server application
architecture. An MTA implements both the client and server portions of
the Simple Mail Transfer Protocol.
A message transfer agent receives mail from either another MTA, a mail submission agent (MSA), or a mail user agent (MUA). The transmission details are specified by the Simple Mail Transfer Protocol
(SMTP). When a recipient mailbox of a message is not hosted locally,
the message is relayed, that is, forwarded to another MTA. Every time an
MTA receives an email message, it adds a Received trace header field to the top of the header of the message,[4]
thereby building a sequential record of MTAs handling the message. The
process of choosing a target MTA for the next hop is also described in
SMTP, but can usually be overridden by configuring the MTA software with
specific routes.
An MTA works in the background, while the user usually interacts directly with a mail user agent. One may distinguish initial submission as first passing through an MSA – port 587 is used for communication between an MUA and an MSA, while port 25 is used for communication between MTAs, or from an MSA to an MTA;[5] this distinction is first made in RFC 2476.
For recipients hosted locally, the final delivery of email to a recipient mailbox is the task of a message delivery agent (MDA). For this purpose the MTA transfers the message to the message handling service component of the message delivery agent (MDA). Upon final delivery, the Return-Path field is added to the envelope to record the return path.
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