問77
頻出度★★☆
メールサーバに届いた電子メールをメールソフトで受け取るために使用されるプロトコルはどれか。
平成24年度 秋期 ITパスポート試験 問77
テクノロジ系ネットワーク › 通信プロトコル
This question's explanation and your answers so far.
解説
問 77
Incorrectア
DNS (Domain Name System) is the name resolution mechanism that maps domain names to IP addresses. It can be used to look up the mail server responsible for a destination domain when mail is delivered, but it is not a protocol for receiving the mail message itself from a server, so it is wrong.
Incorrectイ
HTTP (HyperText Transfer Protocol) is the protocol that transfers HTML, images, and the like between a web browser and a web server. In webmail, HTTP is used to display the screen, but that is screen operation of a web service; it is not the standard protocol by which email software receives email from a mail server, so it is wrong.
- ウ
正解 The correct answer is ウ, POP3. POP3 (Post Office Protocol version 3) is a receiving protocol used when a user’s email software (email client) retrieves (downloads) email that has arrived in a mailbox on a mail server. The action in the question, “receiving email that has arrived at a mail server using email software”, is exactly the situation of bringing mail from the inbox on the server side over to the client side, so POP3 is the one that applies. The flow of email can be organized into four stages: the sender’s email software → (sending) → the sending mail server → (server-to-server transfer) → the receiving mail server → (receiving) → the recipient’s email software, and POP3 is what handles that final “receiving” part.
Incorrectエ
SMTP (Simple Mail Transfer Protocol) is a sending protocol used when email software sends mail out to a mail server and when mail servers transfer mail between themselves. It is the opposite of the direction the question asks about (receiving from a server), so it is wrong.
ここがポイント
- The basic way to memorize email protocols is as a pair: “SMTP for sending, POP3 (or IMAP) for receiving”. Once you identify which segment of the mail flow the question points to, the answer is determined.
- Even among receiving protocols there is a difference: POP3 downloads mail from the server to the device and manages it at hand, whereas IMAP manages mail while leaving it on the server, which makes it easy for multiple devices to refer to the same state.
用語