crop-swap-mail-list/cropswap-sendmail.sh

#!/bin/bash
set -euo pipefail
MAIL="$(cat -)"
MAILGROUP=cropswap@shandan.one

declare -A SUBSCRIBED
declare -a actions
update(){
	da="${actions[$1-1]:0:1}"
	db="${2:0:1}"
	alias="${actions[$1-1]#?}"
	email="${2#?}"
	[ "$da" == "$db" ] || exit 1 # corrupt list
	if [ "$da" == "+" ]; then
		SUBSCRIBED["$email"]="$alias"
	else
		SUBSCRIBED["$email"]=""
	fi
}

exec 4<> "${SLIST}.txt"
flock 4
mapfile -t -c 2 -C update -u 4 actions
for email in "${!SUBSCRIBED[@]}"; do
	if [ -z "${SUBSCRIBED["$email"]}" ]; then
		 continue
	fi
	echo "+${SUBSCRIBED["$email"]}"
	echo "+$email"
done > "${SLIST}".txt
flock -u 4

for email in "${!SUBSCRIBED[@]}"; do
	if [ -z "${SUBSCRIBED["$email"]}" ] || [ "${email,,}" == "${NOFORWARD,,}" ]; then
		 continue
	fi
	echo "Forwarding mail to: ${SUBSCRIBED["$email"]} <${email}>"
	formail -kb \
		-X "MIME-Version:" \
		-X "Content-Type:" \
		-X "Subject:" \
		-X "Date:" \
	<<<"${MAIL}" | /usr/sbin/sendmail \
		-F "${FROM}" \
		-f "${MAILGROUP}" "${SUBSCRIBED["$email"]} <${email}>"
done
#TODO: report errors properly