/usr/bin/mailsubj is in qmail 1.06-4.
This file is owned by root:qmail, with mode 0o755.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 | #!/bin/sh
# WARNING: This file was auto-generated. Do not edit!
subject="$1"
shift
( echo Subject: "$subject"
echo To: ${1+"$@"}
echo ''
cat
) | /var/lib/qmail/bin/qmail-inject
|