sendmail

#!/bin/bash
#########################################
#NRW Nullmailer Rewrite Wrapper V1.3
#Sets all mails to come from user@domain.come
#Replaces all local mail to Admin_Address, prevents that e.g. root@gmail.com gets the mail intented for you

#Version 1.1 23.03.2019
#Changelog
#Bugfixes, if [ -z "$found" ] '"' were missing
#Mails to localUsers like from cron are now rewritten

#Changelog V1.2 28.03.2019
#Bugfix Mails from "root" to "root" are now re-written correctly

#Changelog V1.3 05.01.2023
#Bugfix rewriting mails for root@<hostname> works now

#########################################
#Begin change here
#Where should the mails come from
#example mail address: my@company.com
export NULLMAILER_USER=yourmailaddressprefix  #example: my
export NULLMAILER_HOST=yourMailDomain #example: company.com

#Where should mails go that are directed for local users like "root" or "pi"
Admin_Address=yourMailAdress@yourMailDomain.com # e.g. my@company.com or alertqueue@example.net This address is idependent of sender address
#End change here
#############################################

export NULLMAILER_FLAGS=ft

stdin=`cat`

found=$(echo "$stdin" | head -n5 | grep -i ^to:.*@.*) #Search whether in To @ is present if not, we have to rewrite address. Only To: in the first 5 lines is searched

if [ ! -z "$found" ]
then
#check if @hostname (root@hostname or root@hostname.org), then we have to rewrite
localuser=$(echo "$stdin" | head -n5 | grep -i ^to:.*@${HOSTNAME}[.].*)
	if [ ! -z "$localuser" ]
	then
		found=""
	fi
fi

if [ -z "$found" ]
then
	userToReplace=$(echo "$stdin" | head -n5 | grep -i -P "(?<=^To: ).*")
	replaceString="To: $Admin_Address"
	stdin="${stdin/$userToReplace/$replaceString}"
fi

optPosition=0 #defaultvalue when not found

while getopts ":f:" from; do
    case $from in
        f) optPosition=$OPTIND
           break
           ;;
    esac
done

arguments=($@)

if (($optPosition != 0)); then #-f Option was used
 arguments[(($optPosition-2))]=$NULLMAILER_USER@$NULLMAILER_HOST
 set -- "${arguments[@]}"
fi

#case where user is specified in commandline, example from cron "-i -FCronDaemon -B8BITMIME -oem pi"
#now we search for strings in command line at the end without "@" and replace them with Admin_Address
#we also could use another Wrapper-Script for nullmailer-inject adding the -h option meaning using only message header as recipient address
#see http://manpages.ubuntu.com/manpages/trusty/man1/nullmailer-inject.1.html

localRecipient=$(echo "$@" | grep -Po '\s(\w)+$')

if [ -n "$localRecipient" ] #we must take action and rewrite
then
	arguments="$@"
	lengthArgs=$(expr length "$arguments")
	lengthRecipient=$(expr length "$localRecipient")
	count=$((lengthArgs-lengthRecipient))
	argsNew=$(expr substr "$arguments" 1 $count)
	argsNew="$argsNew $Admin_Address"
	set -- $argsNew 
	#Just to mention, original args are not directly preserved if someone would have called sendmail "-foo bar" 
	#in original "-foo bar" was in $1, now in $1 would be "-foo" and in $2 "bar". However here this shouldn't matter 
fi

echo "$stdin" | /usr/sbin/sendmail-bin "$@"