Postfix cron based rate limiting / throttling with mail alert and automatic postfix shutdown on abnormal queue size

README.md

NOTHING WORKED, postfix does not want to throttle outgoing emails.NO MORE

This will delay sending emails and put extra load on the cpu

Why, you ask?

My server normaly sends 1000-2000 emails per day, one day a client got hacked and sent out 2million of them Outgoing email workload is fairly predictable in my case

Instructions

add in /etc/postfix/main.cf and copy header_checks to the same location
"header_checks = regexp:/etc/postfix/header_checks"

make your own txt files or use sendmail directry the current postqueue.sh -will release 4 mails every 1 minute -alert when mailq is over 10 -alert and stop postfix when queue is over 100

postqueue.sh borrowed and adapted from https://lists.nongnu.org/archive/html/monit-general/2015-01/msg00037.html

Now all outgoing email goes to HOLD queue except those that contain the secret mailfrom then gets moved on incoming by the following cron

setup root cron
* * * * * sh /root/postqueue.sh > /dev/null 2>&1

header_checks

# Do not indent the patterns between "if" and "endif".
#/etc/postfix/header_checks
if /^From:/
!/^From: thoushallnotbeheld@example.com/ HOLD 9988:DEFAULTHOLD
endif

postqueue.sh

#!/bin/bash
postfix_queue=`mailq | grep Requests | awk {'print $5'}`
if [ -z "$postfix_queue" ]
then
	postfix_queue="0";
fi
if [ "$postfix_queue" -le "10" ]
then
        #all is quite
        #http://serverfault.com/questions/408482/postfix-hold-queue-release-x-oldest-messages-or-all-messages-queued-before-x-da
        mailq |egrep "^[[:alnum:]]{10}\!" |sort -k 4,4M -k 5,5n -k 6,6|head -4|awk '{print "mv /var/spool/postfix/hold/" substr($1, 1, length($1)-1) " /var/spool/postfix/incoming/" substr($1, 1, length($1)-1)}'|sh
        /usr/sbin/postfix flush
        echo 'OK'
        exit 0
elif [ "$postfix_queue" -ge "10" ] && [ "$postfix_queue" -le "20" ]
then
        #picking up some load better mail me with special header
        echo 'SEMI'
	mailq |egrep "^[[:alnum:]]{10}\!" |sort -k 4,4M -k 5,5n -k 6,6|head -4|awk '{print "mv /var/spool/postfix/hold/" substr($1, 1, length($1)-1) " /var/spool/postfix/incoming/" substr($1, 1, length($1)-1)}'|sh
        /usr/sbin/postfix flush
	/usr/sbin/sendmail -vt < /root/semi-mail.txt
        exit 1
else
        #Hell breaks loose
        #mail me with special header
        #wait 3 sec for mail delivery
        /usr/sbin/sendmail -vt < /root/high-mail.txt
        /usr/sbin/postfix flush
	sleep 10s
        /usr/sbin/service postfix stop
	#stop postfix
        echo 'FAIL'
        exit 2
fi