Rmail and Coding Systems
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 (see 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 (see 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.
|
