問58
頻出度★★★
電子メールで使用される MIME (Multipurpose Internet Mail Extensions) に関する記述として, 適切なものはどれか。
平成22年度 春期 ITパスポート試験 問58
テクノロジ系ネットワーク › ネットワーク応用
This question's explanation and your answers so far.
解説
問 58
- ア
正解 The correct answer is ア, “A method for sending attachments such as image files via email.” SMTP, which is used to send email, was originally specified so that it could carry only 7-bit ASCII text (letters, digits, and symbols). As it is, it cannot send binary data such as image, audio, or document files, nor non-ASCII characters such as Japanese. The extension created to remove this restriction is MIME (Multipurpose Internet Mail Extensions). MIME adds headers to a mail message, such as Content-Type (the kind of data; for example, image/jpeg) and Content-Transfer-Encoding (the encoding method; for example, base64), and it embeds binary data in the body after converting it into an ASCII string with Base64 or the like. It can also split the body and the attachments into several parts (multipart) and combine them into a single mail message. It is only thanks to this mechanism that email with attachments works at all, so ア is appropriate as a description of MIME.
Incorrectイ
A method for encrypting and sending email using public-key cryptography is a description of S/MIME or PGP. MIME itself is no more than a framework for expressing the kind of data and the encoding method; it has no encryption or digital signature functions. S/MIME has a similar name, but it is a separate standard that builds on MIME and adds encryption and digital signature functions, so care is needed not to confuse it with MIME itself.
Incorrectウ
A method for writing the body in HTML so as to achieve layout and design is a description of HTML mail. When HTML mail is sent, the part where text/html is specified as the Content-Type does indeed use the MIME mechanism, but that is only one example of the data formats MIME can carry. The purpose of MIME is to carry data in a wide variety of formats with the kind of data clearly indicated, not to achieve visual layout and design, so it is not appropriate as a description of MIME.
Incorrectエ
A method for forwarding (receiving) email from a mail server to a user’s terminal is a description of receiving protocols such as POP3 and IMAP. MIME is a data-format convention that defines how the contents of a mail message are represented; it is not a communication procedure for exchanging mail between a server and a terminal. Note that sending mail and delivering it between servers is the job of SMTP.
ここがポイント
- Definition of MIME: an extension that encodes non-ASCII characters and binary data (images, audio, video, and so on) that SMTP cannot handle, using Base64 or the like, and states their kind explicitly with Content-Type so that they can be sent by email. It is the very mechanism that makes attachments possible.
- How the email-related terms divide up: sending and delivery between servers is SMTP, receiving from a server to a terminal is POP3 or IMAP, encryption and digital signatures are S/MIME or PGP, and extending the data format is MIME. If you sort out which role each choice is describing, you will not get lost.
用語