post_install() {
	if ! getent group postdrop &>/dev/null; then
		groupadd -g 75 postdrop >/dev/null
	fi
	if ! getent group postfix &>/dev/null; then
		groupadd -g 73 postfix >/dev/null
	fi
	if ! getent passwd postfix &>/dev/null; then
		useradd -u 73 -d /var/spool/postfix -g postfix -G adm -s /bin/nologin postfix >/dev/null
	fi
	if ! groups postfix | grep adm &>/dev/null; then
		gpasswd -a postfix adm >/dev/null
	fi
	postfix_shell=$(getent passwd postfix | cut -d: -f7)
	if [ "$postfix_shell" != '/bin/nologin' ]; then
		chsh -s /bin/nologin postfix &>/dev/null
	fi
	if [ ! -d /var/spool/postfix/public/pickup ]; then
		mkfifo /var/spool/postfix/public/pickup
	fi
}

post_upgrade() {
	post_install
	if [[ $(vercmp $2 3.0.0-3) -eq -1 ]]; then
		echo '==> The postfix daemon binaries have moved.'
		echo '==> Please restart postfix as soon as possible.'
	elif [[ $(vercmp $2 3.0.1-1) -eq -1 ]]; then
		echo '==> Several Postfix-internal protocols have changed.'
		echo '==> Please restart postfix as soon as possible.'
	fi
}

post_remove() {
	if getent passwd postfix &>/dev/null; then
		userdel postfix >/dev/null
	fi
	if getent group postfix &>/dev/null; then
		groupdel postfix >/dev/null
	fi
	if getent group postdrop &>/dev/null; then
		groupdel postdrop >/dev/null
	fi
}