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<TITLE>MHonArc v2.5 -- Appendix: MIME Conformance
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<H1><a name=
"appendix-mimeconf">Appendix: MIME Conformance
</a></H1>
<P>This appendix describes how well MHonArc implements
MIME-conformance as defined in
<a href=
"http://www.pobox.com/~ehood/MIME/2049/rfc2049.html">
RFC
2049: (MIME) Part Five: Conformance Criteria and Examples
</a>.
Also, additional MIME-related features are summarized.
<li><a href=
"#mime-conformance">MIME-Conformance
</a>
<li><a href=
"#otherstuff">Other Stuff Supported
</a>
<H2><a name=
"mime-conformance">MIME-Conformance
</a></H2>
<p>MIME-conformance is defined in section
2 of
<a href=
"http://www.pobox.com/~ehood/MIME/2049/rfc2049.html">
RFC
2049: (MIME) Part Five: Conformance Criteria and Examples
</a>.
Following is the text extracted from section
2 of RFC
2049 with
annotations added on how MHonArc conforms to each criteria listed.
It should be noted that the criteria listed in RFC
2049 is geared
towards interactive MUAs; therefore, some criteria may not be
<table border=
0 cellpadding=
4>
<td><strong>NOTE
</strong></td>
<td><p>All notes about conformance is based upon the default MIME-related
<a href=
"resources/mimefilters.html">MIMEFILTERS
</a>,
<a href=
"resources/charsetconverters.html">CHARSETCONVERTERS
</a>,
<a href=
"resources/mimeargs.html">MIMEARGS
</a>
Always generate a
"MIME-Version: 1.0" header field in
<table border=
0 cellpadding=
4>
<td><strong><img src=
"monicon.png" alt=
"MHonArc"></strong></td>
Recognize the Content-Transfer-Encoding header field
and decode all received data encoded by either quoted-printable or base64 implementations. The identity
transformations
7bit,
8bit, and binary must also be
<table border=
0 cellpadding=
4>
<td><strong><img src=
"monicon.png" alt=
"MHonArc"></strong></td>
<td><p>Base64, quoted-printable,
7bit,
8bit, and binary are supported.
Also, uuencode is supported:
<tt>uuencode
</tt>,
<tt>x-uuencode
</tt>, and
Any non-
7bit data that is sent without encoding must be
properly labelled with a content-transfer-encoding of
8bit or binary, as appropriate. If the underlying
transport does not support
8bit or binary (as SMTP
[RFC-
821] does not), the sender is required to both
encode and label data using an appropriate Content-Transfer-Encoding such as quoted-printable or base64.
<table border=
0 cellpadding=
4>
<td><strong><img src=
"monicon.png" alt=
"MHonArc"></strong></td>
Must treat any unrecognized Content-Transfer-Encoding
as if it had a Content-Type of
"application/octet-stream", regardless of whether or not the actual
Content-Type is recognized.
<table border=
0 cellpadding=
4>
<td><strong><img src=
"monicon.png" alt=
"MHonArc"></strong></td>
<td><p>Currently, MHonArc will still call the registered
<a href=
"resources/mimefilters.html">content-type filter
</a> for the specified
Content-Type, but the
<b><tt>$isdecoded
</tt></b> will be set to a false
value. With the default set of filters, the
<b><tt>$isdecoded
</tt></b>flag is ignored. Therefore, behavior could be considered undefined when
MHonArc process a message with an unrecognized Content-Transfer-Encoding.
Recognize and interpret the Content-Type header field,
and avoid showing users raw data with a Content-Type
field other than text. Implementations must be able
to send at least text/plain messages, with the
character set specified with the charset parameter if
<table border=
0 cellpadding=
4>
<td><strong><img src=
"monicon.png" alt=
"MHonArc"></strong></td>
<td><p>MHonArc conforms to the first sentence of the paragraph
The second sentence is not applicable.
Ignore any content type parameters whose names they do
<table border=
0 cellpadding=
4>
<td><strong><img src=
"monicon.png" alt=
"MHonArc"></strong></td>
Explicitly handle the following media type values, to
at least the following extents:
<li><p>Recognize and display
"text" mail with the
character set
"US-ASCII."<table border=
0 cellpadding=
4>
<td><strong><img src=
"monicon.png" alt=
"MHonArc"></strong></td>
<li><p>Recognize other character sets at least to the
extent of being able to inform the user about what
character set the message uses.
<table border=
0 cellpadding=
4>
<td><strong><img src=
"monicon.png" alt=
"MHonArc"></strong></td>
<td><p>Not really applicable. Warnings are generated during processing
if a character set is encountered that is not recognized.
<li><p>Recognize the
"ISO-8859-*" character sets to the
extent of being able to display those characters that
are common to ISO-
8859-* and US-ASCII, namely all
characters represented by octet values
1-
127.
<table border=
0 cellpadding=
4>
<td><strong><img src=
"monicon.png" alt=
"MHonArc"></strong></td>
<li><p>For unrecognized subtypes in a known character
set, show or offer to show the user the
"raw" version
of the data after conversion of the content from
canonical form to local form.
<table border=
0 cellpadding=
4>
<td><strong><img src=
"monicon.png" alt=
"MHonArc"></strong></td>
<td><p>MHonArc will treat the data as text/plain and convert.
<li><p>Treat material in an unknown character set as if
it were
"application/octet-stream".
<table border=
0 cellpadding=
4>
<td><strong><img src=
"monicon.png" alt=
"MHonArc"></strong></td>
<td><p>No. A warning is generated for unknown character sets. The
data will be shown in raw form, with HTML special characters converted
to entity references. This behavior is the default because some MUAs
are known to give incorrect charset parameters.
<li><p>At a minumum provide facilities to treat any
unrecognized subtypes as if they were
"application/octet-stream".
<table border=
0 cellpadding=
4>
<td><strong><img src=
"monicon.png" alt=
"MHonArc"></strong></td>
<td><p>All image, audio, and video types are saved to an external file
with a link to the file created in the HTML. For applicable image types, they
are inlined unless the image has an attachment content-disposition.
<li><p>Offer the ability to remove either of the quoted-printable or base64 encodings defined in this
document if they were used and put the resulting
information in a user file.
<table border=
0 cellpadding=
4>
<td><strong><img src=
"monicon.png" alt=
"MHonArc"></strong></td>
<td><p>Most application types are decoded and saved to an external file
with a link to the file created in the HTML. Some application types
can be converted directly to HTML.
<li><p>Recognize the mixed subtype. Display all relevant
information on the message level and the body part
header level and then display or offer to display
each of the body parts individually.
<table border=
0 cellpadding=
4>
<td><strong><img src=
"monicon.png" alt=
"MHonArc"></strong></td>
<td><p>Yes. Each part is automatically processed according to its
<li><p>Recognize the
"alternative" subtype, and avoid
showing the user redundant parts of
multipart/alternative mail.
<table border=
0 cellpadding=
4>
<td><strong><img src=
"monicon.png" alt=
"MHonArc"></strong></td>
<li><p>Recognize the
"multipart/digest" subtype,
specifically using
"message/rfc822" rather than
"text/plain" as the default media type for body parts
inside
"multipart/digest" entities.
<table border=
0 cellpadding=
4>
<td><strong><img src=
"monicon.png" alt=
"MHonArc"></strong></td>
<li><p>Treat any unrecognized subtypes as if they were
<table border=
0 cellpadding=
4>
<td><strong><img src=
"monicon.png" alt=
"MHonArc"></strong></td>
<li><p>Recognize and display at least the RFC822 message
encapsulation (message/rfc822) in such a way as to
preserve any recursive structure, that is, displaying
or offering to display the encapsulated data in
accordance with its media type.
<table border=
0 cellpadding=
4>
<td><strong><img src=
"monicon.png" alt=
"MHonArc"></strong></td>
<li><p>Treat any unrecognized subtypes as if they were
"application/octet-stream".
<table border=
0 cellpadding=
4>
<td><strong><img src=
"monicon.png" alt=
"MHonArc"></strong></td>
<li><p>Upon encountering any unrecognized Content-Type field,
an implementation must treat it as if it had a media
type of
"application/octet-stream" with no parameter
sub-arguments. How such data are handled is up to an
implementation, but likely options for handling such
unrecognized data include offering the user to write it
into a file (decoded from its mail transport format) or
offering the user to name a program to which the
decoded data should be passed as input.
<table border=
0 cellpadding=
4>
<td><strong><img src=
"monicon.png" alt=
"MHonArc"></strong></td>
<td><p>Yes. The data is passed to the
<a href=
"resources/mimefilters.html#m2h_external">m2h_external::filter
</a>
to be saved to an external file.
<li><p>Conformant user agents are required, if they provide
non-standard support for non-MIME messages employing
character sets other than US-ASCII, to do so on
received messages only. Conforming user agents must not
send non-MIME messages containing anything other than
<p>In particular, the use of non-US-ASCII text in mail
messages without a MIME-Version field is strongly
discouraged as it impedes interoperability when sending
messages between regions with different localization
conventions. Conforming user agents MUST include proper
MIME labelling when sending anything other than plain
text in the US-ASCII character set.
<table border=
0 cellpadding=
4>
<td><strong><img src=
"monicon.png" alt=
"MHonArc"></strong></td>
<a href=
"resources/mimefilters.html#m2h_text_plain">m2h_text_plain::filter
</a>
supports an option to specify what character set to use if no character
set is specified. By default, ISO-
8859-
1 is assumed.
<p>In addition, non-MIME user agents should be upgraded if
at all possible to include appropriate MIME header
information in the messages they send even if nothing
else in MIME is supported. This upgrade will have
little, if any, effect on non-MIME recipients and will
aid MIME in correctly displaying such messages. It
also provides a smooth transition path to eventual
adoption of other MIME capabilities.
<table border=
0 cellpadding=
4>
<td><strong><img src=
"monicon.png" alt=
"MHonArc"></strong></td>
<li><p>Conforming user agents must ensure that any string of
non-white-space printable US-ASCII characters within a
"*text" or
"*ctext" that begins with
"=?" and ends with
"?=" be a valid encoded-word. (
"begins" means: At the
start of the field-body or immediately following
linear-white-space;
"ends" means: At the end of the
field-body or immediately preceding linear-white-space.) In addition, any
"word" within a
"phrase" that
begins with
"=?" and ends with
"?=" must be a valid
<table border=
0 cellpadding=
4>
<td><strong><img src=
"monicon.png" alt=
"MHonArc"></strong></td>
<li><p>Conforming user agents must be able to distinguish
encoded-words from
"text",
"ctext", or
"word"s,
according to the rules in section
4, anytime they
appear in appropriate places in message headers. It
must support both the
"B" and
"Q" encodings for any
character set which it supports. The program must be
able to display the unencoded text if the character set
is
"US-ASCII". For the ISO-
8859-* character sets, the
mail reading program must at least be able to display
the characters which are also in the US-ASCII set.
<table border=
0 cellpadding=
4>
<td><strong><img src=
"monicon.png" alt=
"MHonArc"></strong></td>
<td><p>MHonArc supports non-ASCII encoding of text in message headers,
including the
"B" and
"Q" encodings. By default, US-ASCII,
ISO-
8859-[
1-
10], and ISO-
2022-JP are supported. For encoded
words with an unrecognized character set, the word is left in
encoded form. Additional character set support can be added via the
<a href=
"resources/charsetconverters.html">CHARSETCONVERTERS
</a> resource.
<H2><a name=
"otherstuff">Other Stuff Supported
</a></H2>
<p>The following lists other MIME-related features supported
<li><p>Support for uuencoding as a Content-Transfer-Encoding.
<li><p>Support for many media-types (including the ability to extend
that support). For a complete list, along with more
<a href=
"resources/mimefilters.html">MIMEFILTERS
</a> resource.
Note, many media-types cannot be directly converted into HTML. For
these types, they are saved to a separate file with a link to the
file inserted in the converted HTML message data.
<li><p>Support for
<b><tt>multipart/related
</tt></b> by allowing
<a href=
"resources/mimefilters.html">filters
</a> to access other
message parts via content-ids.
<li><p>Support for
<b><tt>cid:
</tt></b> URLs in
<b><tt>text/html
</tt></b>
data. The provides support for things like MHTML:
<em>MIME E-mail Encapsulation of Aggregate Documents
</em>,
<a href=
"http://www.ietf.org/rfc/rfc2110.txt">RFC
2110</a>.
<a href=
"http://www.ietf.org/rfc/rfc2369.txt">RFC
2369</a>,
<em>The Use of URLs as Meta-Syntax for Core Mail List Commands
and their Transport through Message Header Fields
</em>. The
URLs in list header fields will be converted into hypertext links.
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$Date:
2001/
12/
24 14:
38:
07 $
<br><img align=
"top" src=
"monicon.png" alt=
"">
<a href=
"http://www.mhonarc.org/"><strong>MHonArc
</strong></a><br>
Copyright
© 1999,
<a href=
"http://www.mhonarc.org/~ehood/">Earl Hood
</a>,
<a href=
"mailto:mhonarc@mhonarc.org"
>mhonarc@mhonarc.org
</a><br>
projects / OpenSPARC-T2-DV / blob