/usr/lib/courier/mkesmtpdcert is in courier-mta 0.73.1-1.6.
This file is owned by root:root, with mode 0o755.
The actual contents of the file can be viewed below.
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 | #! /bin/bash
#
#
# Copyright 2000-2007 Double Precision, Inc.  See COPYING for
# distribution information.
#
# This is a short script to q`uickly generate a self-signed X.509 key for
# ESMTP STARTTLS.  Normally this script would get called by an automatic
# package installation routine.
PEMFILE="$1"
if [ -z "$PEMFILE" ]; then
	PEMFILE=/usr/lib/courier/esmtpd.pem
fi
if test "openssl" = "openssl"
then
	test -x /usr/bin/openssl || exit 0
else
	test -x /usr/local/bin/certtool || exit 0
fi
if test -f "$PEMFILE"
then
	echo "$PEMFILE already exists."
	exit 1
fi
cleanup() {
	rm -f "$PEMFILE".rand
	rm -f "$PEMFILE"
	rm -f "$PEMFILE".key
	rm -f "$PEMFILE".cert
	exit 1
}
cd /usr/lib/courier
umask 077
BITS="$BITS"
set -e
if test "openssl" = "openssl"
then
	cp /dev/null "$PEMFILE"
	chmod 600 "$PEMFILE"
	chown daemon "$PEMFILE"
	dd if=/dev/urandom of="$PEMFILE".rand count=1 2>/dev/null
	/usr/bin/openssl req -new -x509 -days 365 -nodes \
		  -config /etc/courier/esmtpd.cnf -out "$PEMFILE" -keyout "$PEMFILE" || cleanup
	/usr/bin/openssl gendh -rand "$PEMFILE".rand 512 >>"$PEMFILE" || cleanup
	/usr/bin/openssl x509 -subject -dates -fingerprint -noout -in "$PEMFILE" || cleanup
	rm -f "$PEMFILE".rand
else
	echo "/usr/local/bin/certtool is not supported in debian"
	exit 1
	if test "$BITS" = ""
	then
		BITS="high"
	fi
	cp /dev/null /usr/lib/courier/esmtpd.key
	chmod 600 /usr/lib/courier/esmtpd.key
	cp /dev/null /usr/lib/courier/esmtpd.cert
	chmod 600 /usr/lib/courier/esmtpd.cert
	/usr/local/bin/certtool --generate-privkey --sec-param=$BITS --outfile esmtpd.key
	/usr/local/bin/certtool --generate-self-signed --load-privkey esmtpd.key --outfile esmtpd.cert --template /etc/courier/esmtpd.cnf
	cp /dev/null /usr/lib/courier/esmtpd.pem
	chmod 600 /usr/lib/courier/esmtpd.pem
	chown daemon /usr/lib/courier/esmtpd.pem
	cat esmtpd.key esmtpd.cert >esmtpd.pem
	rm -f esmtpd.key esmtpd.cert
fi
 |