You can check whether the mail() is working inside your server by creating a mail.php file inside your public_html directory.

$to = “”;
$subject = “Hi!”;
$body = “Hi,nnHow are you?”;
if (mail($to, $subject, $body)) {
echo(“<p>Message successfully sent!</p>”);
} else {
echo(“<p>Message delivery failed…</p>”);

Check if any php script is causing the mass mailing with
cd /var/spool/exim/input

egrep “X-PHP-Script” * -R

Following command will show path to the script being utilized to send mail
ps -C exim -fH eww
ps -C exim -fH eww | grep home

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