問82
頻出度★★☆
PC1のメールクライアントから PC2のメールクライアントの利用者宛ての電子メールを送信するとき，①～③で使われているプロトコルの組合せとして，適切なものはどれか。 電子メールは次の経路で送られる。 - ①：PC1 → メールサーバ - ②：メールサーバ → メールサーバ - ③：メールサーバ → PC2
平成31年度 春期 ITパスポート試験 問82
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 82
Incorrectア
①POP3, ②POP3, ③SMTP — all three are reversed. ① is PC1 sending the email out, so it should be SMTP for sending, and the server-to-server relay at ② should also be SMTP, but this option makes both of them POP3. Conversely, ③ is reception by the client, so it should be POP3, yet it is set to SMTP; the assignment of sending and receiving is completely swapped.
Incorrectイ
①POP3, ②SMTP, ③SMTP. The SMTP at ② (server-to-server relay) is correct, but ① is sending yet is set to POP3 (should be SMTP), and ③ is reception by the client yet is set to SMTP (should be POP3); these two places, ① and ③, are wrong.
Incorrectウ
①SMTP, ②POP3, ③POP3. The SMTP at ① (sending) and the POP3 at ③ (client reception) match the correct answer and are right; the only error is setting the server-to-server relay at ② to POP3. The relay that sends email out from a server to the destination server uses SMTP.
- エ
正解 Judge by the division of roles: SMTP is used for sending and relaying email, while POP3 is used when a client receives (retrieves) email from a server. ① is where PC1's mail client sends the email out to its own mail server, so it is SMTP. ② is where the sending mail server relays the email to the destination mail server; transfer between servers is also a form of sending, so it is SMTP. ③ is where PC2's mail client retrieves (receives) the email that has arrived at its own mail server, so it is POP3. Therefore the combination ①SMTP, ②SMTP, ③POP3, which is choice エ, is correct.
ここがポイント
- Grasp the division of roles: SMTP is used for sending email and relaying it between servers, while POP3 (or IMAP) is used for the reception where a client retrieves email from a server.
- Tracing the path, it is easier to tell them apart if you remember that the push from the sending client → server → server is all SMTP, and only the final server → receiving client is POP3.
用語