Chapter 10. the Internet

84

  Content Transfer Encoding:

Now

MIME Version

is 1.0 and thus all MIME mails have a header like this:

MIME Version: 1.0

Content Type

describes the type of content. For example, an usual mail with Japanese text has

a header like that:

Content Type: text/plain; charset="iso 2022 jp"

Available types are described in RFC 2046 (

http://www.faqs.org/rfcs/rfc2046.html

).

Content Transfer Encoding

describes the way to convert the contents. Available values are

BINARY

,

7bit

,

8bit

,

BASE64

, and

QUOTED PRINTABLE

. Since SMTP cannot handle 8bit data,

8bit

and

BINARY

cannot be used. ESMTP can use them. Base64 and quoted printable are ways

to convert 8bit data into 7bit and 8bit data have to be converted using either of them to sent by

SMTP.

RFC 2046 (

http://www.faqs.org/rfcs/rfc2046.html

) describes media type and sub type

for

Content Type

header. Available types are

text

,

image

,

audio

,

video

, and

application

.

Now we are interested in

text

because we are discussing about i18n. Sub types for

text

are

plain

,

enriched

,

html

, and so on.

charset

parameter can also be added to specify encodings.

US ASCII

,

ISO 8859 1

,

ISO 8859 2

, . . . ,

ISO 8859 10

are defined by RFC 2046 (

http://

www.faqs.org/rfcs/rfc2046.html

) for

charset

. This list can be added by writing a new

RFC.

  RFC 1468 (

http://www.faqs.org/rfcs/rfc1468.html

)

ISO 2022 JP

  RFC 1554 (

http://www.faqs.org/rfcs/rfc1554.html

)

ISO 2022 JP 2

  RFC 1557 (

http://www.faqs.org/rfcs/rfc1557.html

)

ISO 2022 KR

  RFC 1922 (

http://www.faqs.org/rfcs/rfc1922.html

)

ISO 2022 CN

  RFC 1922 (

http://www.faqs.org/rfcs/rfc1922.html

)

ISO 2022 CN EXT

  RFC 1842 (

http://www.faqs.org/rfcs/rfc1842.html

)

HZ GB 2312

  RFC 1641 (

http://www.faqs.org/rfcs/rfc1641.html

)

UNICODE 1 1

  RFC 1642 (

http://www.faqs.org/rfcs/rfc1642.html

)

UNICODE 1 1 UTF 7

  RFC 1815 (

http://www.faqs.org/rfcs/rfc1815.html

)

ISO 10646 1