/etc/nmh/components is in nmh 1.6-2.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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%; Our default components file. Used by `comp'
%;
%;
%; This line creates our From: header based on the following ordering:
%;
%; - Use a -from switch if it exists ({from})
%; - Use our local mailbox identity; first from the Local-Mailbox profile
%; entry, otherwise gets the information from the local system
%;
%<{from}%|%(void(localmbox))%>%(void(width))%(putaddr From: )
%;
%; Here we include an address list if one or more "-to" arguments were
%; given, otherwise just output a blank header. We do the same for the
%; "cc" header as well.
%;
%<{to}%(void(width))%(putaddr To: )%|To:%>
%<{cc}%(void(width))%(putaddr cc: )%|cc:%>
%;
%; Slight difference here: if we're not given "-fcc" on the command line,
%; make the default mailbox +outbox
%;
Fcc: %<{fcc}%(putstr)%|+outbox%>
Subject:%<{subject} %(putstr)%>
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