Catching spammer

exim -bp | exiqsumm | more
exim -bpr | grep "<*@*>" | awk '{print $4}'|grep -v "<>" | sort | uniq -c | sort -n

That will show you the maximum no of email currently in the mail queue have from or to the email address in the mail queue with exact figure.

exim -bpr | grep "<*@*>" | awk '{print $4}'|grep -v "<>" |awk -F "@" '{ print $2}' | sort | uniq -c | sort -n

That will show you the maximum no of email currently in the mail queue have for the domain or from the domain with number.

Check if any php script is causing the mass mailing with

cd /var/spool/exim/input
egrep "X-PHP-Script" * -R

Just cat the ID that you get and you will be able to check which script is here causing problem for you.