howto's

You may check first what is the path of sendmail:
whereis sendmail or php -i | grep sendmail
move /usr/sbin/sendmail to something like /usr/sbin/sendmail.or
vi /usr/sbin/sendmail
put the code below:

#!/usr/bin/perl
# use strict;
use Env;
my $date = `date`;
chomp $date;
open (INFO, ">>/var/log/formmail.log") || die "Failed to open file ::$!";
my $uid = $>;
my @info = getpwuid($uid);
if($REMOTE_ADDR) {
print INFO "$date - $REMOTE_ADDR ran $SCRIPT_NAME at $SERVER_NAME \n";
}
else {
print INFO "$date - $PWD - @info\n";
}
my $mailprog = '/usr/sbin/sendmail.or';
foreach (@ARGV) {
$arg="$arg" . " $_";
}
open (MAIL,"|$mailprog $arg") || die "cannot open $mailprog: $!\n";
while (<STDIN> ) {
print MAIL;
}
close (INFO);
close (MAIL);


chmod a+x /usr/sbin/sendmail
touch /var/log/formmail.log
and chmod 777 /var/log/formmail.log

that should be all.