dmarc-peek.sh

#! /usr/bin/env bash
#! /bin/bash
set -e

 # associative arrays requre bash v4; here's cute way to find it
if [ ${BASH_VERSINFO[0]} -lt 4 ]
# BEWARE! exec in a subshell doesn't. So we must use `for shell in
# $(which -a bash)` instead of `which -a bash |while read shell`.
then for shell in $(which -a bash)
do if [ $("$shell" -c 'echo ${BASH_VERSINFO[0]}') -ge 4 ]
then exec "$shell" "$0" "$@"
fi done fi

declare -A p_none p_quarantine p_reject

#
# sniffing various DMARC policies in the wild
#
main() {
	echo ';Collecting DMARC policies...'
	while read d
	do	txt=$(dig +short _dmarc.$d txt |grep '^"v=') # that grep excludes CNAMES
		if [ "$txt" == "" ] # retry once (in case we had a temp DNS failure)
		then txt=$(dig +short _dmarc.$d txt |grep '^"v=')
		fi

		if [[ $txt =~ [\ \;\"]p=none ]]
		then p_none[$d]="$txt"
		elif [[ $txt =~ [\ \;\"]p=quarantine ]]
		then p_quarantine[$d]="$txt"
		elif [[ $txt =~ [\ \;\"]p=reject ]]
		then p_reject[$d]="$txt"
		fi
	done < <(do_lynx) # process substitution preserves global variables

	echo $'\n;PERMISSIVE/GATHERING:'
	for d in "${!p_none[@]}"
	do printf ";_dmarc.%-25s TXT %s\n" "$d" "${p_none[$d]}"
	done |sort

	echo $'\n;QUARANTINE:'
	for d in "${!p_quarantine[@]}"
	do printf ";_dmarc.%-25s TXT %s\n" "$d" "${p_quarantine[$d]}"
	done |sort

	echo $'\n;REJECT:'
	for d in "${!p_reject[@]}"
	do printf ";_dmarc.%-25s TXT %s\n" "$d" "${p_reject[$d]}"
	done |sort

	echo
}

do_lynx() {
	lynx -dump https://dmarc.org/who-is-using-dmarc/ |awk '
		/^     \* .+ \(.+\)/ {
			start=match($0,/\(/)+1
			stop=match($0,/\)/)
			d=substr($0,start,stop-start)
			split(d,a,/, /)
			for(d in a) {
				print a[d]
			}
		}
	'
}

# dump the list
main
exit

# or look for something spectific
#main |grep -i returnpath.net
#exit

# or generate some stats
main |cut -c40- |tr -d '\\ "' |awk -F ';' '
	{
		for(i=1;i<=NF;i++)
			if($i)
				print$i
	}
' |sort |uniq -c |sort -n