MH-MIME(7)MH-MIME(7)NAMEmh-mime - Overview of nmh(7) MIME message composition and display
DESCRIPTION
The acronym MIME stands for Multipurpose Internet Mail Extensions, the
format of Internet messages used to send multi-media content. The nmh
command suite has support for the display and composition of MIME mes‐
sages, but currently MIME support is not completely integrated into all
tools. This document provides an overview as to which tools support
MIME message display, storage, and composition.
Local Character Set Conversion
All of the nmh commands convert non-native character sets to the local
character set, as specified by the operating system locale settings.
See locale(1) for more details on the environment variables used to set
the local character set. Character set conversion will only take place
if nmh was built with iconv(3) support. See the mhparam(1) man page
for how determine whether your nmh installation includes iconv(3) sup‐
port.
Depending on the source and target character set, it may not be possi‐
ble to convert all characters to the local character set. In this case
a substitution character will be used for the characters that cannot be
converted.
Message Display
The default format used by scan(1) will automatically decode MIME-
encoded headers. If you have a custom scan format, see the examples
provided with the nmh distribution (found in the “/usr/local/etc/nmh”
directory) and mh-format(5) for details on how to make sure your MIME
headers are properly decoded.
By default, if show detects that it is reading a MIME message it will
invoke mhshow(1). The default behavior of mhshow is to only display
text parts that are not marked as attachments. See mhshow(1) for
details on how to control what mhshow will display.
Message Interrogation and Storage
The mhlist(1) command will display a listing of the MIME parts con‐
tained within a message. That information can be used in conjunction
with the mhstore command to save individual parts or content types of a
message. See mhlist(1) and mhstore(1) for more details on how these
commands work.
Message Composition and Reply
All messages sent by send(1) will automatically be processed by
mhbuild(1) before being passed to post(1) for message submission.
Mhbuild will use the locale settings to mark text content with the
appropriate character set and apply any necessary encoding. If you
wish to include text in your message using a character set that does
not match your locale, you will need to specify the character set using
a mhbuild directive; see mhbuild(1) for more information.
For attaching files or composing other non-text content, there are two
options: the attach system and mhbuild directives.
The attach system is best suited for content where one or more files
are being attached to a message. You can use the attach system by
either using the attach command at the “What now?” prompt, or by
inserting an “Attach:” header in the message draft containing the name
of the file you wish to attach to the message (it should be noted all
that the attach command does is place an “Attach” header in the message
draft). Mhbuild will then automatically include the specified file(s)
in the outgoing message. See send(1) for details on how mhbuild deter‐
mines the proper content type of attached files.
The other method of composing MIME messages is to use mhbuild direc‐
tives. This allows exact control over the contents and format of the
MIME message, but has a more complicated syntax. mhbuild(1) contains
details on the directive syntax and examples of directives for differ‐
ent media types. It is important to note that when using mhbuild
directives the user must run mhbuild outside of send to have it process
directives; when being run by send, mhbuild is configured to not
process directives so normal user text is not mistaken for a directive.
When using directives a user typically uses the mime command at the
“What now?” prompt to process them.
When replying to messages using repl(1) the traditional MH method of
including the original text in the reply does not interoperate with
MIME messages. As of this writing there is no native solution for
addressing this issue, but the contrib directory
(/usr/local/share/doc/nmh/contrib) contains a Perl program called
replyfilter which will decode text parts and present them in an appro‐
priate manner to be included in a message reply. See the comments at
the top of replyfilter for instructions on how to configure nmh to work
with it.
Message Rewrite
The mhfixmsg(1) command can apply various transformations to MIME mes‐
sages, including decoding of text parts, converting the character set
of text parts, and insertion of text/plain parts to correspond to text
parts of other subtypes. mhfixmsg can also repair defects in MIME mes‐
sages, such as mismatched top-level boundary indicators and invalid
Content-Transfer-Encoding values.
SEE ALSOcomp(1), iconv(3), mh-format(5)mhbuild(1), mhfixmsg(1), mhparam(1),
nmh(7), repl(1), whatnow(1),
/usr/local/share/doc/nmh/contrib/replyfilter
BUGS
MIME support should be more integrated into all of the nmh tools than
it currently is.
nmh-1.6 March 16, 2014 MH-MIME(7)
