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(emacs)Rmail Coding

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Rmail and Coding Systems
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   Rmail automatically decodes messages which contain non-ASCII
characters, just as Emacs does with files you visit and with subprocess
output.  Rmail uses the standard `charset=CHARSET' header in the
message, if any, to determine how the message was encoded by the
sender.  It maps CHARSET into the corresponding Emacs coding system
(Note: Coding Systems), and uses that coding system to decode message
text.  If the message header doesn't have the `charset' specification,
or if CHARSET is not recognized, Rmail chooses the coding system with
the usual Emacs heuristics and defaults (Note: Recognize Coding).

   Occasionally, a message is decoded incorrectly, either because Emacs
guessed the wrong coding system in the absence of the `charset'
specification, or because the specification was inaccurate.  For
example, a misconfigured mailer could send a message with a
`charset=iso-8859-1' header when the message is actually encoded in
`koi8-r'.  When you see the message text garbled, or some of its
characters displayed as empty boxes, this may have happened.

   You can correct the problem by decoding the message again using the
right coding system, if you can figure out or guess which one is right.
To do this, invoke the `M-x rmail-redecode-body' command.  It reads
the name of a coding system, encodes the message body using whichever
coding system was used to decode it before, then redecodes it using the
coding system you specified.  If you specified the right coding system,
the result should be readable.

   Decoding and encoding using the wrong coding system is lossless for
most encodings, in particular with 8-bit encodings such as iso-8859 or
koi8.  So, if the initial attempt to redecode the message didn't result
in a legible text, you can try other coding systems until you succeed.

   With some coding systems, notably those from the iso-2022 family,
information can be lost in decoding, so that encoding the message again
won't bring back the original incoming text.  In such a case,
`rmail-redecode-body' cannot work.  However, the problems that call for
use of `rmail-redecode-body' rarely occur with those coding systems.
So in practice the command works when you need it.