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... the fact that they limit the contents of electronic mail messages to
relatively short lines of seven-bit ASCII. This forces users to
...
... forces users to
convert any non-textual data that they may wish to send into seven-
bit bytes representable as printable ASCII characters before invoking
a local mail UA ...
... Content-Types which could usefully be transported via email are
represented, in their "natural" format, as 8-bit character or binary
data. Such data cannot be transmitted over some transport protocols.
...
... For example, RFC 821std10(-> 2821prop) restricts mail messages to 7-bit US-ASCII data
with lines no longer than 1000 characters.
...
... It is necessary, therefore, to define a standard mechanism for re-
encoding such data into a 7-bit short-line format. This document
specifies that such encodings will be indicated by a new "Content-
...
... binary data and the desire for a readable
encoding of data that is mostly, but not entirely, 7-bit data. For
this reason, at least two encoding mechanisms are necessary: a
...
... Content-Transfer-Encoding field is designed to specify an
invertible mapping between the "native" representation of a type of
data and a representation that can be readily exchanged using 7 bit
mail transport protocols, such as those defined by RFC 821std10(-> 2821prop) ...
... bAsE64 are all equivalent. An encoding type of 7BIT requires that
the body is already in a seven-bit mail-ready representation. This
is the default value -- that is, "Content-Transfer-Encoding ...
... 8bit" means that the lines are short, but there may be
non-ASCII characters (octets with the high-order
bit set).
"Binary" means that not only may non-ASCII ...
...
The difference between "8bit" (or any other conceivable bit-width
token) and the "binary" token ...
... CRLF semantics,
while the bit-width tokens do require such adherence. If the body
contains data in any bit ...
... bit-width tokens do require such adherence. If the body
contains data in any bit-width other than 7-bit, the appropriate
bit ...
... tokens do require such adherence. If the body
contains data in any bit-width other than 7-bit, the appropriate
bit-width Content-Transfer-Encoding ...
... bit-width other than 7-bit, the appropriate
bit-width Content-Transfer-Encoding token must be used (e.g., "8bit ...
... token must be used (e.g., "8bit"
for unencoded 8 bit wide data). If the body contains binary data,
the "binary" Content-Transfer-Encoding ...
... entity is of type "multipart" or "message", the Content-Transfer-
Encoding is not permitted to have any value other than a bit width
(e.g., "7bit", "8bit", etc.) or "binary".
...
... mechanisms described here are mechanisms for encoding arbitrary octet
streams, not bit streams. If a bit stream is to be encoded via one
of these mechanisms, it must first be converted to an 8-bit ...
... encoding arbitrary octet
streams, not bit streams. If a bit stream is to be encoded via one
of these mechanisms, it must first be converted to an 8-bit byte
...
... bit streams. If a bit stream is to be encoded via one
of these mechanisms, it must first be converted to an 8-bit byte
stream using the network ...
... bit order ("big-endian"), in which
the earlier bits in a stream become the higher-order bits in a byte.
...
... the earlier bits in a stream become the higher-order bits in a byte.
A bit stream not ending at an 8-bit ...
... stream become the higher-order bits in a byte.
A bit stream not ending at an 8-bit boundary must be padded with
zeroes. This document provides a mechanism for noting the addition
...
... higher-order bits in a byte.
A bit stream not ending at an 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 ...
... Content-Type/transport
combinations and not for others. (For example, in an 8-bit
transport, no encoding ...
... character sets, while such encodings are clearly required for 7-
bit SMTP.) Second, certain Content-Types may require different
...
... example, many PostScript bodies might consist entirely of short
lines of 7-bit data and hence require little or no encoding.
Other PostScript ...
... following rules:
Rule #1: (General 8-bit representation) Any octet, except those
indicating a line break according to the newline convention of the
...
...
A 65-character subset of US-ASCII is used, enabling 6 bits to be
represented per printable character. (The extra 65th character, "=",
is used to signify a special processing function.)
...
... encoding process represents 24-bit groups of input bits as output
strings of 4 encoded characters. Proceeding from left to right, a
24-bit ...
... bits as output
strings of 4 encoded characters. Proceeding from left to right, a
24-bit input group is formed by concatenating 3 8-bit input groups ...
... groups.
These 24 bits are then treated as 4 concatenated 6-bit groups, each
of which is translated into a single digit in the base64 ...
... encoding a bit stream via the base64 encoding, the bit stream
must be presumed to be ordered with the most-significant-bit first.
...
... base64 encoding, the bit stream
must be presumed to be ordered with the most-significant-bit first.
That is, the first bit ...
... That is, the first bit in the stream will be the high-order bit in
the first byte, and the eighth bit will be the low-order bit ...
... stream will be the high-order bit in
the first byte, and the eighth bit will be the low-order bit in the
first byte, and so on.
...
... high-order bit in
the first byte, and the eighth bit will be the low-order bit in the
first byte, and so on.
...
... first byte, and so on.
Each 6-bit group is used as an index into an array of 64 printable
characters. The character referenced by the index is placed in the
...
... under some circumstances.
Special processing is performed if fewer than 24 bits are available
at the end of the data being encoded. A full encoding quantum is
...
... at the end of the data being encoded. A full encoding quantum is
always completed at the end of a body. When fewer than 24 input bits
are available in an input group, zero bits ...
... bits
are available in an input group, zero bits are added (on the right)
to form an integral number of 6-bit groups ...
... group, zero bits are added (on the right)
to form an integral number of 6-bit groups. Padding at the end of
the data is performed using the '=' character. Since all base64 ...
... arise: (1) the final quantum of encoding input is an integral
multiple of 24 bits; here, the final unit of encoded output will be
an integral multiple of 4 characters with no "=" padding, (2) the
final quantum of encoding ...
... an integral multiple of 4 characters with no "=" padding, (2) the
final quantum of encoding input is exactly 8 bits; here, the final
unit of encoded output will be two characters followed by two "="
padding characters, or (3) the final quantum of encoding ...
... padding characters, or (3) the final quantum of encoding input is
exactly 16 bits; here, the final unit of encoded output will be three
characters followed by one "=" padding character.
...
... RFC-1340] review and approval. Note that if the
specified character set includes 8-bit data, a Content-Transfer-
Encoding header field and a corresponding encoding ...
... header field. "US-
ASCII" does not indicate an arbitrary seven-bit character code, but
specifies that the body uses character coding that uses the exact
correspondence of codes to characters specified in ASCII ...
... using code-switching procedures (e.g., those of ISO 2022), as well
as 8-bit or multiple octet character encodings MUST use an
appropriate character set ...
... 8bit", or "binary" is permitted for
entities of type "multipart". The multipart delimiters and header
fields are always represented as 7-bit ASCII in any case (though the
header fields ...
... quoted-printable, a problem might arise if message/partial
entities are constructed in an environment that supports binary or
8-bit transport. The problem is that the binary data would be split
...
... transport. If such objects were encountered at a gateway into a 7-
bit transport environment, there would be no way to properly encode
them for the 7-bit ...
... bit transport environment, there would be no way to properly encode
them for the 7-bit world, aside from waiting for all of the parts,
reassembling the message, and then encoding the reassembled data in
...
...
transfer-encoding of 7-bit (the default). In particular, even in
environments that support binary or 8-bit transport ...
... transfer-encoding of 7-bit (the default). In particular, even in
environments that support binary or 8-bit transport, the use of a
content-transfer-encoding ...
... message/external-body must always have a content-transfer-encoding of
7-bit (the default). In particular, even in environments that
support binary or 8-bit transport ...
... 7-bit (the default). In particular, even in environments that
support binary or 8-bit transport, the use of a content-transfer-
encoding ...
...
Note that since the external bodies are not transported as mail, they
need not conform to the 7-bit and line length requirements, but might
in fact be binary files. Thus a Content-Transfer-Encoding ...
... any automatic processing.
PADDING -- the number of bits of padding that were appended to the
bit-stream comprising the actual contents to produce the enclosed
...
... PADDING -- the number of bits of padding that were appended to the
bit-stream comprising the actual contents to produce the enclosed
byte-oriented data. This is useful for enclosing a bit-stream in
...
... bit-stream comprising the actual contents to produce the enclosed
byte-oriented data. This is useful for enclosing a bit-stream in
a body when the total number of bits is not a multiple of the byte
...
... byte-oriented data. This is useful for enclosing a bit-stream in
a body when the total number of bits is not a multiple of the byte
size.
...
... or base64 implementations. Encode any data sent that is not in
seven-bit mail-ready representation using one of these
transformations and include the appropriate Content-Transfer-
Encoding header ...
... Encoding header field, unless the underlying transport mechanism
supports non-seven-bit data, as SMTP does not.
...
... Coded Character Set--7-Bit American Standard Code for Information Interchange, ANSI X3.4-1986. ...
... International Standard--Information Processing--ISO 7-bit and 8-bit coded character sets--Code extension techniques, ISO ...
... International Standard--Information Processing--ISO 7-bit and 8-bit coded character sets--Code extension techniques, ISO 2022:1986. ...
... Information Processing -- 8-bit Single-Byte Coded Graphic Character Sets -- Part 1: Latin Alphabet No. 1, ISO 8859-1:1987. Part 2: Latin alphabet No. 2, ISO 8859-2 ...
... International Standard--Information Processing--ISO 7-bit coded character set for information interchange, ISO 646:1983. ...