General :: Add PHP User As Trusted Sender In Sendmail?

I have a mail script that has been running on my website for several years. One problem I had with the script was when a bad address was put in, the mail was rejected to the server rather than to the sender. I have now recently added a fifth parameter to the mail script using the -f sendmail option to set the return path.

PHP Code:

$mailsend=mail("$email","$subject","$emess","$ehead","-f$adminEmail");

The PHP manual says this:

Quote:

The user that the webserver runs as should be added as a trusted user to the sendmail configuration to prevent a 'X-Warning' header from being added to the message when the envelope sender (-f) is set using this method. For sendmail users, this file is /etc/mail/trusted-users. I do have the 'X-Warning' header on e-mails sent with this script and have asked my server administrator for some help in adding "the user that the Web server runs as" as a trusted user.