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content type
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... which is presumed to lack such a field.
2. A Content-Type header field, generalized from RFC 1049hist [RFC-1049 ...
... encoding) of such data.
2.a. A "text" Content-Type value, which can be used to represent
textual information in a number of character sets and
...
... manner.
2.b. A "multipart" Content-Type value, which can be used to
combine several body parts, possibly of differing types of
data, into a single message.
...
... data, into a single message.
2.c. An "application" Content-Type value, which can be used to
transmit application data or binary data ...
... file transfer
service.
2.d. A "message" Content-Type value, for encapsulating another
mail message.
...
... MIME has been carefully designed as an extensible mechanism, and it
is expected that the set of content-type/subtype pairs and their
associated parameters will grow significantly with time. Several
other MIME ...
... notation.
It must be noted that Content-Type values, subtypes, and parameter
names as defined in this document are case-insensitive. However,
...
... MIME type might use a
"version" parameter in the content-type field if necessary.
NOTE TO IMPLEMENTORS ...
... header fields defined in this document,
including MIME-Version, Content-type, etc., are subject to the
general syntactic rules for header fields ...
... The Content-Type Header Field ...
...
The purpose of the Content-Type field is to describe the data
contained in the body fully enough that the receiving user agent ...
... user, or otherwise deal with the data in an appropriate manner.
HISTORICAL NOTE: The Content-Type header field was first defined in
RFC 1049hist ...
... here.
The Content-Type header field is used to specify the nature of the
data in the body of an entity ...
...
In general, the top-level Content-Type is used to declare the general
type of data, while the subtype specifies a specific format for that
type of data. Thus, a Content-Type ...
... Content-Type is used to declare the general
type of data, while the subtype specifies a specific format for that
type of data. Thus, a Content-Type of "image/xyz" is enough to tell
a user agent ...
... are "global" in the sense that they might apply to any subtype. For
example, the "boundary" parameter makes sense only for the
"multipart" content-type, but the "charset" parameter might make
sense with several content-types ...
... In the Augmented BNF notation of RFC 822std11(-> 2822prop), a Content-Type header field
value is defined as follows:
...
... value is defined as follows:
content := "Content-Type" ":" type "/" subtype *(";"
parameter)
; case-insensitive ...
... subtype
names is the desire that their uses must not conflict. That is, it
would be undesirable to have two different communities using
"Content-Type: application/foobar" to mean two different things. The
process of defining new content-subtypes, then, is not intended to be
a mechanism for imposing restrictions, but simply a mechanism for
...
... a mechanism for imposing restrictions, but simply a mechanism for
publicizing the usages. There are, therefore, two acceptable
mechanisms for defining new Content-Type subtypes:
1. Private values (starting ...
... message -- an encapsulated message. A body of
Content-Type "message" is itself all or part of a
fully formatted RFC 822std11(-> 2822prop) conformant message which
...
... fully formatted RFC 822std11(-> 2822prop) conformant message which
may contain its own different Content-Type header
field. The primary subtype is "rfc822". The
"partial" subtype is defined for partial messages,
...
... US-ASCII character set, which can be explicitly specified as
"Content-type: text/plain; charset=us-ascii". If no Content-Type ...
... Content-type: text/plain; charset=us-ascii". If no Content-Type is
specified, this default is assumed. In the presence of a MIME-
...
... sender's intent might have been otherwise.
RATIONALE: In the absence of any Content-Type header field or
MIME-Version ...
... aware that if a message lacks both the MIME-Version and the
Content-Type header fields, it may in practice contain almost
anything.
...
... anything.
It should be noted that the list of Content-Type values given here
may be augmented in time, via the mechanisms described above, and
that the set of subtypes is expected to grow substantially.
...
... that the set of subtypes is expected to grow substantially.
When a mail reader encounters mail with an unknown Content-type
value, it should generally treat it as equivalent to
"application/octet-stream ...
... NOTE: The five values defined for the Content-Transfer-Encoding
field imply nothing about the Content-Type other than the
algorithm by which it was encoded or the transport ...
... 8-bit boundary must be padded with
zeroes. This document provides a mechanism for noting the addition
of such padding in the case of the application Content-Type, which
has a "padding" parameter.
...
... encodings other than "7bit", "8bit", or "binary" with any Content-
Type that recursively includes other Content-Type fields, notably the
"multipart" and "message" Content-Types. All encodings ...
...
NOTE ON THE RELATIONSHIP BETWEEN CONTENT-TYPE AND CONTENT-
TRANSFER-ENCODING: It may seem that the Content-Transfer-Encoding ...
... TRANSFER-ENCODING: It may seem that the Content-Transfer-Encoding
could be inferred from the characteristics of the Content-Type
that is to be encoded, or, at the very least, that certain
Content-Transfer-Encodings ...
... transports used for mail, some
encodings may be appropriate for some Content-Type/transport
combinations and not for others. (For example, in an 8-bit ...
... represented using a binary transport encoding. Finally, since
Content-Type is intended to be an open-ended specification
mechanism, strict specification of an association ...
... application protocol with a specific lower-level transport.
This is not desirable since the developers of a Content-Type
should not have to be aware of all the transports in use and what
...
... Content-ID value has special
semantics in the case of the multipart/alternative content-type.
This is explained in the section of this document dealing with
multipart/alternative.
...
... The Predefined Content-Type Values ...
...
This document defines seven initial Content-Type values and an
extension mechanism for private or experimental types. Further
...
... The Text Content-Type ...
...
The text Content-Type is intended for sending material which is
principally textual in form. It is the default Content-Type. A
...
... The text Content-Type is intended for sending material which is
principally textual in form. It is the default Content-Type. A
"charset" parameter may be used to indicate the character set ...
... subtype, "text/plain", which indicates plain (unformatted) text. The
default Content-Type for Internet mail is "text/plain; charset ...
...
A critical parameter that may be specified in the Content-Type field
for text/plain data is the character set ...
... user agents explicitly
specify a character set via the Content-Type header field. "US-
ASCII ...
... earlier version of the American Standard. Insofar as one of the
purposes of specifying a Content-Type and character set is to
permit the receiver ...
... character set used, if anything other than US-ASCII,
must always be explicitly specified in the Content-Type field.
No other character set ...
...
The primary subtype of text is "plain". This indicates plain
(unformatted) text. The default Content-Type for Internet mail,
"text/plain ...
... No other text subtype is defined by this document.
The formal grammar for the content-type header field for text is as
follows:
...
... The Multipart Content-Type ...
... allowed and is a body part for which all default values are to be
assumed. In such a case, the absence of a Content-Type header field
implies that the corresponding body is plain US-ASCII text ...
... encapsulated message, the body of which is an image. In order to
represent the latter, the body part must have "Content-Type:
message", and its body (after the blank line) must be the
encapsulated ...
... message", and its body (after the blank line) must be the
encapsulated message, with its own "Content-Type: image" header
field. The use of similar syntax facilitates the conversion of
...
... given in Appendix C.
The Content-Type field for multipart entities requires one parameter,
"boundary", which is used to specify the encapsulation boundary. The
...
... two hyphen characters ("-", decimal code 45) followed by the boundary
parameter value from the Content-Type header field.
...
... type field is such that it is often necessary to enclose the
boundaries in quotes on the Content-type line. This is not always
necessary, but never hurts. Implementors should be sure to study the
...
... necessary, but never hurts. Implementors should be sure to study the
grammar carefully in order to avoid producing illegal Content-type
fields. Thus, a typical multipart Content-Type header field ...
... grammar carefully in order to avoid producing illegal Content-type
fields. Thus, a typical multipart Content-Type header field might
look like this:
...
... look like this:
Content-Type: multipart/mixed;
boundary=gc0p4Jq0M2Yt08jU534c0p
...
... But the following is illegal:
Content-Type: multipart/mixed;
boundary=gc0p4Jq0M:2Yt08jU534c0p
...
... (because of the colon) and must instead be represented as
Content-Type: multipart/mixed;
boundary="gc0p4Jq0M:2Yt08jU534c0p"
...
... CRLFs, in which case there are no header fields for the next part
(and it is therefore assumed to be of Content-Type text/plain).
...
... It does NOT end with a linebreak.
--simple boundary
Content-type: text/plain; charset=us-ascii
...
... This is the epilogue. It is also to be ignored.
The use of a Content-Type of multipart in a body part within another
multipart entity is explicitly allowed. In such cases, for obvious
...
... example of nested multipart entities.
The use of the multipart Content-Type with only a single body part
may be useful in certain contexts, and is explicitly permitted.
...
...
The only mandatory parameter for the multipart Content-Type is the
boundary parameter, which consists of 1 to 70 characters from a set
of characters known to be very robust through email ...
...
delimiter := "--" boundary CRLF ; taken from Content-Type field.
; There must be no space
; between "--" and boundary.
...
... MIME-Version: 1.0
Content-Type: multipart/alternative; boundary=boundary42
--boundary42
...
... version of message goes here....
--boundary42
Content-Type: text/richtext
.... RFC 1341(-> 1521(-> 2049draft | 2048(-> 4289 | 4288) | 2047draft | 2046draft | 2045draft)) ...
... version of same message goes here ...
--boundary42
Content-Type: text/x-whatever
.... fanciest formatted version ...
... the semantics are different. In particular, in a digest, the default
Content-Type value for a body part is changed from "text/plain" to
"message/rfc822". This is done to allow a more readable digest
...
... Subject: Internet Digest, volume 42
Content-Type: multipart/digest;
boundary="---- next message ----"
...
... multipart/mixed".
The formal grammar for content-type header fields for multipart data
is given by:
...
... The Message Content-Type ...
... encapsulate another
mail message. For this common operation, a special Content-Type,
"message", is defined. The primary subtype, message/rfc822, has no
required parameters in the Content-Type ...
... Content-Type,
"message", is defined. The primary subtype, message/rfc822, has no
required parameters in the Content-Type field. Additional subtypes,
"partial" and "External-body", do have required parameters. These
subtypes are explained below.
...
...
A Content-Type of "message/rfc822" indicates that the body contains
an encapsulated message, with the syntax of an RFC 822std11(-> 2822prop) ...
... agents limit the size of individual messages that can be sent.
Content-Type "message/partial" thus indicates that the body contains
a fragment of a larger message.
...
... fragment of a larger message.
Three parameters must be specified in the Content-Type field of type
message/partial: The first, "id", is a unique identifier, as close to
...
... header fields:
Content-Type: Message/Partial;
number=2; total=3;
id="oc=jpbe0M2Yt4s@thumper.bellcore.com"
...
... id="oc=jpbe0M2Yt4s@thumper.bellcore.com"
Content-Type: Message/Partial;
id="oc=jpbe0M2Yt4s@thumper.bellcore.com";
number=2
...
... But part 3 MUST specify the total number of parts:
Content-Type: Message/Partial;
number=3; total=3;
id="oc=jpbe0M2Yt4s@thumper.bellcore.com"
...
... MIME entity, which may have its
own Content-Type header field, and thus may contain any other data
type.
...
... Message-ID: <id2@host.com>
Content-type: message/partial;
id="ABC@host.com"; number=2; total=2
...
... following message:
Content-type: message/external-body; access-
type=local-file;
...
... security reasons, such an id and
password are not specified as content-type parameters, but must be
obtained from the user.
...
... Because mail servers accept a variety of syntaxes, some of which is
multiline, the full command to be sent to a mail server is not
included as a parameter on the content-type line. Instead, it is
provided as the "phantom body" when the content-type is
...
... included as a parameter on the content-type line. Instead, it is
provided as the "phantom body" when the content-type is
message/external-body ...
... trailing area must simply be ignored. However, it is a convenient
place for additional data that cannot be included in the content-type
header field. In particular, if the "access-type" value is "mail-
...
... message header fields which appear in the body of the
message/external-body data must be used to declare the Content-type
of the external body if it is anything other than plain ASCII text,
...
... Message-ID: <id1@host.com>
Content-Type: multipart/alternative; boundary=42
Content-ID: <id001@guppylake.bellcore.com>
...
...
--42
Content-Type: message/external-body;
name="BodyFormats.ps";
...
... expiration="Fri, 14 Jun 1991 19:13:14 -0400 (EDT)"
Content-type: application/postscript
Content-ID ...
... expiration="Fri, 14 Jun 1991 19:13:14 -0400 (EDT)"
Content-type: application/postscript
Content-ID ...
...
--42
Content-Type: message/external-body;
access-type=mail-server
...
... expiration="Fri, 14 Jun 1991 19:13:14 -0400 (EDT)"
Content-type: application/postscript
Content-ID ...
... headers on the outer and inner parts must be merged
using the same rules as for message/partial. In particular, this
means that the Content-type header is overridden, but the From and
Subject ...
... ignored for most access-types.
The formal grammar for content-type header fields for data of type
message is given by:
...
... The Application Content-Type ...
...
The "application" Content-Type is to be used for data which do not
fit in any of the other categories, and particularly for data to be
processed by mail-based uses of application programs. This is
...
... processed by mail-based uses of application programs. This is
information which must be processed by an application before it is
viewable or usable to a user. Expected uses for Content-Type
application include mail-based file transfer, spreadsheets, data for
...
...
Such applications may be defined as subtypes of the "application"
Content-Type. This document defines two subtypes: octet-stream, and
PostScript ...
... path-search mechanism whereby an arbitrary program named in the
Content-Type parameter (e.g., an "interpreter=" parameter) is found
and executed using the mail body as input.
...
... The Image Content-Type ...
... IANA, as described in Appendix E.
The formal grammar for the content-type header field for data of type
image ...
... The Audio Content-Type ...
...
A Content-Type of "audio" indicates that the body contains audio
data. Although there is not yet a consensus on an "ideal" audio ...
... channel is assumed.
The formal grammar for the content-type header field for data of type
audio ...
...
A Content-Type of "video" indicates that the body contains a time-
varying-picture image, possibly with color and coordinated sound ...
... audio, and this is explicitly permitted for subtypes of "video".
The formal grammar for the content-type header field for data of type
video is given by:
...
... Experimental Content-Type Values ...
...
A Content-Type value beginning with the characters "X-" is a private
value, to be used by consenting mail systems by mutual agreement.
...
... cases, the discussion of the application/postscript content-type in
Section 7.4.2 may serve as a model for considering other content-
types with remote execution capabilities.
...
... SMTP does not.
3. Recognize and interpret the Content-Type header field, and
avoid showing users raw data with a Content-Type ...
... Content-Type header field, and
avoid showing users raw data with a Content-Type field other than
text. Be able to send at least text/plain messages, with the
...
... US-ASCII.
4. Explicitly handle the following Content-Type values, to at
least the following extents:
...
...
5. Upon encountering any unrecognized Content- Type, an
implementation must treat it as if it had a Content-Type of
"application/octet-stream" with no parameter sub-arguments. How
...
...
The following guidelines may be useful to anyone devising a data
format (Content-Type) that will survive the widest range of
networking technologies and known broken MTAs ...
...
--unique-boundary-1
Content-Type: multipart/parallel;
boundary=unique-boundary-2
...
...
--unique-boundary-1
Content-type: text/richtext
This is <bold><italic>richtext.</italic></bold>
...
...
--unique-boundary-1
Content-Type: message/rfc822
From: (mailbox ...
... CRLF;Again,no space by "--",
content := "Content-Type" ":" type "/" subtype *(";" parameter)
; case-insensitive matching of type and subtype
...
...
delimiter := "--" boundary CRLF ;taken from Content-Type field.
; There must be no space
; between "--" and boundary.
...
... MIME has been carefully designed to have extensible mechanisms, and
it is expected that the set of content-type/subtype pairs and their
associated parameters will grow significantly with time. Several
other MIME ...
... registry for such values.
In general, parameters in the content-type header field are used to
convey supplemental information for various content types ...
... convey supplemental information for various content types, and their
use is defined when the content-type and subtype are defined. New
parameters should not be defined as a way to introduce new
functionality.
...
... E.1 Registration of New Content-type/subtype Values ...
...
Content-type: text
Subtypes defined by this document: plain
...
...
________________________________________________________
Content-type: multipart
Subtypes defined by this document: mixed, alternative,
...
...
________________________________________________________
Content-type: message
Subtypes defined by this document: rfc822, partial, external-body
...
... permitted for other subtypes of "message".
______________________________________________________________
Content-type: application
Subtypes defined by this document: octet-stream ...
... security
problems.
________________________________________________________________
Content-type: image
...
... base64 generally preferred
________________________________________________________________
Content-type: audio
...
... base64 generally preferred
________________________________________________________________
Content-type: video
Subtypes defined by this document: mpeg
...
... attribute information, is converted to a
universal canonical form. The specific content type of the body as
well as its associated attributes dictate the nature of the canonical
form that is used. Conversion to the proper canonical form ...
... character set conversion is involved, however,
care must be taken to understand the semantics of the content-type,
which may have strong implications for any character set conversion,
...
... A Content-Transfer-Encoding appropriate for this body is applied.
Note that there is no fixed relationship between the content type and
the transfer encoding. In particular, it may be appropriate to base
...