mh-forward-subject-format

mh-forward-subject-format is a variable defined in `mh-e.el'.
Its value is

"%s: %s"

Documentation:
*Format string for forwarded message subject.

This option is a string which includes two escapes ("%s"). The
first "%s" is replaced with the sender of the original message,
and the second one is replaced with the original "Subject:".

You can customize this variable.

This variable was introduced, or its default value was changed, in version 6.0 of the MH-E package that is part of Emacs 22.1.