問69
頻出度★★☆
図のメールの送受信で利用されるプロトコルの組合せとして，適切なものはどれか。 - メールクライアント → メールサーバ：①メール送信 - メールサーバ → メールクライアント：②メール受信 - メールサーバ ↔ メールサーバ：③メール転送
平成21年度 秋期 ITパスポート試験 問69
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 69
Incorrectア
This makes (1), (2), and (3) all POP3, but POP3 is a receive-only protocol for retrieving mail from a mailbox on the mail server. Sending from the client to the server in (1) and forwarding between servers in (3) cannot be done with POP3.
Incorrectイ
This makes (1) POP3 and (2) SMTP, so sending and receiving are completely reversed. Furthermore, forwarding between servers in (3) is also given as POP3, but forwarding is a sending action, so SMTP is correct. All three are wrong.
- ウ
正解 The correct answer is ウ ((1) SMTP, (2) POP3, (3) SMTP). In (1), the mail client sends mail out to its own mail server, and the protocol used for sending is SMTP (Simple Mail Transfer Protocol). In (3), mail servers relay mail from one to another; this is also a «sending» action from server to server, so SMTP is used here as well. On the other hand, (2) is the case where the mail client goes to the mail server to pick up the mail addressed to it, so POP3 (Post Office Protocol version 3), the protocol for receiving (retrieving), is used. In short, the rule is «SMTP for every sending direction, POP3 only for the receiving direction», so ウ with (1) SMTP, (2) POP3, (3) SMTP matches the figure.
Incorrectエ
It is correct that (1) and (3) are SMTP, but making (2), the receiving step, SMTP as well is wrong. SMTP is a protocol that pushes mail from the sender to the other party; it cannot be used for the action of a client retrieving mail from a mailbox on the server. POP3 (or IMAP) is needed here.
ここがポイント
- SMTP is the protocol for sending mail, and it is used both for sending from client to server ((1)) and for forwarding from server to server ((3)).
- POP3 is the protocol for receiving mail, used when a client retrieves mail from a mailbox on the mail server ((2)). IMAP is another receiving protocol; the difference from POP3 is that it lets you manage mail while leaving it on the server.
用語