mh-scan-subject-regexp

mh-scan-subject-regexp is a variable defined in `mh-scan.el'.
Its value is

"^ *[0-9]+........[ ]*...................\\([Rr][Ee]\\(\\[[0-9]+\\]\\)?:\\s-*\\)*\\([^<\n]*\\)"

Documentation:
This regular expression matches the subject.

It must match from the beginning of the line. Note that the
default setting of `mh-folder-font-lock-keywords' expects this
expression to contain at least three parenthesized expressions.
The first is expected to match the "Re:" string, if any, and is
highlighted with the face `mh-folder-followup'. The second
matches an optional bracketed number after "Re:", such as in
"Re[2]:" (and is thus a sub-expression of the first expression)
and the third is expected to match the subject line itself which
is highlighted with the face `mh-folder-subject'. For example,
the default (broken on multiple lines for readability) is

^ *[0-9]+........[ ]*...................
\\([Rr][Ee]\\(\\[[0-9]+\\]\\)?:\\s-*\\)*
\\([^<\n]*\\)

This regular expression should be correct as it is needed by
non-fontification functions.