/usr/lib/qmail/boot/binm1+df is in qmail 1.06-5.
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 10 11 | #!/bin/sh
# Using splogger to send the log through syslog.
# Using dot-forward to support sendmail-style ~/.forward files.
# Using binmail to deliver messages to /var/spool/mail/$USER by default.
# Using BSD 4.4 binmail interface: /usr/libexec/mail.local -r
exec env - PATH="/var/lib/qmail/bin:$PATH" \
qmail-start '|dot-forward .forward
|preline -f /usr/libexec/mail.local -r "${SENDER:-MAILER-DAEMON}" -d "$USER"' \
splogger qmail
|