transport
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... Internet
SMTP transport defined by RFC 821std10(-> 2821prop). As the format has seen wider use,
a number of limitations have proven increasingly restrictive for the
...
... identity
transformation are usually applied to data in order to
allow it to pass through mail transport mechanisms
which may have data or character set limitations. ...
... encoding such data into a 7bit short line format. Proper labelling
of unencoded material in less restrictive formats for direct use over
less restrictive transports is also desireable. This document
specifies that such encodings will be indicated by a new "Content-
...
... the body data, and provide useful information about the sort of
encoding that might be needed for transmission in a given transport
system. The terms "7bit data", "8bit data", and "binary data ...
... domain into material in the "7bit" range, thus making it
safe to carry over restricted transports. The specific definition of
the transformations are given below.
...
... the initial publication of this document, there are no standardized
Internet mail transports for which it is legitimate to include
unencoded binary data in mail bodies. Thus there are no
...
... valid in Internet mail. However, in the event that binary
mail transport becomes a reality in Internet mail, or when MIME is
...
... MIME is
used in conjunction with any other binary-capable mail transport
mechanism, binary bodies must be labelled as such using this
mechanism.
...
... media type other than the algorithm by which
it was encoded or the transport system requirements if unencoded.
...
... or the inner "8bit" labelling placed an unnecessarily high demand on
the transport system because the actual included data were actually
7bit-safe.
...
... media types. There are several
reasons why this is not the case. First, given the varying types of
transports used for mail, some encodings may be appropriate for some
combinations of media types ...
... encodings may be appropriate for some
combinations of media types and transports but not for others. (For
example, in an 8bit transport ...
... transports but not for others. (For
example, in an 8bit transport, no encoding would be required for text
in certain character sets ...
... PostScript's binary encoding mechanism) may only
be reasonably represented using a binary transport encoding.
Finally, since the Content-Type field is intended to be an open-ended ...
... specification of an application protocol with a specific lower-level
transport. This is not desirable since the developers of a media
type should not have to be aware of all the transports in use and
...
... transport. This is not desirable since the developers of a media
type should not have to be aware of all the transports in use and
what their limitations are.
...
... US-ASCII character set. It encodes the data in such a way that
the resulting octets are unlikely to be modified by mail transport.
If the data being encoded are mostly US-ASCII text, the encoded form
...
... must be represented according to Rule #1. This rule is
necessary because some MTAs (Message Transport Agents,
programs which transport ...
... Message Transport Agents,
programs which transport messages from one user to
another, or perform a portion of such transfers) are
known to pad lines of text with SPACEs, and others are
...
... encoding represents something of a
compromise between readability and reliability in transport. Bodies
encoded with the quoted-printable encoding ...
... base64 Content-Transfer-Encoding. A way
to get reasonably reliable transport through EBCDIC gateways is to
...
... between the lines of quoted-printable data may be altered in
transport, in the same manner that plain text mail has always been
altered in Internet mail when passing between systems with differing
...
... transport-padding ...
... transport-padding ...
... *LWSP-char ; Composers MUST NOT generate non-zero length transport padding, but receivers MUST be able to handle padding added by message transports. ...
... non-zero length transport padding, but receivers MUST be able to handle padding added by message transports. ...
... share these properties, and thus do not fulfill the portability
requirements a binary transport encoding for mail must meet.
...
... restrictions imposed by the characteristics of some Internet mail
transport mechanisms (see RFC 2049draft).
...
... transport-padding ...
... transport-padding ...
... *LWSP-char ; Composers MUST NOT generate non-zero length transport padding, but receivers MUST be able to handle padding added by message transports. ...
... non-zero length transport padding, but receivers MUST be able to handle padding added by message transports. ...