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12. Handling MIME types

12.1 How Sylpheed-Claws checks for Mime types

When attaching a file to a message (composing a new message), the MIME type of the attached file is choosen based on the file extension from the mapping list defined in the mime.types file(s). Sylpheed-Claws defines its MIME type mapping table by loading the system wide MIME types file, then the user file. The systeme file is /usr/share/mime/globs or, if this doesn't exist, SYSCONFDIR/mime.types (SYSCONFDIR can be defined at compile time), or if it does not exist, /etc/mime.types

A mime.types file consist of one MIME type definition per line, each definition line starting with the name of the MIME type, followed by a space separated list of the corresponding file extensions. The file can contain empty lines, and comments start with the # character and close at line's end.

Following is a typical mime.types file (an extract of mine):

# This file controls what Internet media types are sent to the client for
# given file extension(s). Sending the correct media type to the client
# is important so they know how to handle the content of the file.
# The Internet media type registry is at
# <>.

# MIME type Extension
application/mac-binhex40 hqx
application/mac-compactpro cpt
application/msword doc
application/pdf pdf
application/postscript ai eps ps
application/rtf rtf
application/x-bcpio bcpio
application/x-bzip2 bz2
application/x-csh csh
application/x-gtar gtar
application/x-gzip gz tgz
application/x-kword kwd kwt
application/x-kspread ksp
application/x-kpresenter kpr kpt
application/x-kchart chrt
application/x-latex latex
application/x-sh sh
application/x-shar shar
application/x-shockwave-flash swf
application/x-tar tar
application/x-tcl tcl
application/x-tex tex
application/x-texinfo texinfo texi
application/x-troff t tr roff
application/x-troff-man man
application/zip zip
audio/mpeg mpga mp2 mp3
audio/x-aiff aif aiff aifc
audio/x-wav wav
image/gif gif
image/ief ief
image/jpeg jpeg jpg jpe
image/png png
image/tiff tiff tif
text/plain asc txt
text/rtf rtf
text/sgml sgml sgm
text/xml xml
video/mpeg mpeg mpg mpe
video/x-msvideo avi
text/html html htm

If the file can be found or has the wrong format, Sylpheed-Claws will assume the default MIME type for all the attachments: application/octet-stream. In such a case, the recipients mail client may not know what application to use to view the attachment.

12.2 How Sylpheed-Claws handles attachments (reception)

When opening an attachment (select the attachment, right click and select Open) Sylpheed-Claws uses one of the following methods to determine the application to launch:

The binding of the applications to each MIME type is defined in the mailcap file. The systeme wide file is /etc/mailcap, while the user file is $HOME/.mailcap.

In the mailcap file, there is one definition per line, big lines can be broken by escaping the newline with a \ character, the first element of the line is the MIME type, then a semi-colon, (;), and finally the application to launch. The application part (right side of the semi-colon) can contain several shell commands separated by an escaped semi-colon (\;) and the %s string is replaced by the name of the file when launching the command.

Following is a typical mailcap file (an extract of mine):

image/*; ee %s

video/mpeg; gtv %s
video/*; xanim %s

application/pdf; xpdf %s

text/html; dillo %s

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