Qmail Sending Issue

Hi Experts,

I have a simple form on our website that when submitted sends an email to webforms@mydomain.com

I am using php mail function

$headers = 'From: webform-submit@mydomain.com' . "\r\n" .
    'Reply-To: webform-submit@mydomain.com' . "\r\n" .
    'X-Mailer: PHP/' . phpversion();

mail (webforms@mydomain.com, subject, body from captured webform, $headers);

I receive the following error in my /psa/var/log/maillog

Oct 27 13:27:17 mydomain qmail-remote-handlers[26056]: Handlers Filter before-remote for qmail started ...
Oct 27 13:27:17 mydomain qmail-remote-handlers[26056]: from=#@[]
Oct 27 13:27:17 mydomain qmail-remote-handlers[26056]: to=postmaster@mydomain.com
Oct 27 13:27:17 mydomain qmail: 1256675237.656456 delivery 1805: failure: Connected_to_(IP OMITTED)_but_sender_was_rejected./Remote_host_said:_501_5.1.7_Bad_sender_address_syntax/
Oct 27 13:27:17 mydomain qmail: 1256675237.656528 status: local 0/10 remote 0/20
Oct 27 13:27:17 mydomain qmail: 1256675237.656559 triple bounce: discarding bounce/175875568
Oct 27 13:27:17 mydomain qmail: 1256675237.656587 end msg 175875568

The strange thing is that if I change the RECIPIENT address (not SENDER address) to my GMAIL account the mail goes directly through.  The log shows the following on a successful send to my GMAIL account.

Oct 27 13:29:20 mydomain qmail-queue-handlers[30393]: Handlers Filter before-queue for qmail started ...
Oct 27 13:29:21 mydomain qmail-queue-handlers[30393]: from=anonymous@mydomain.com
Oct 27 13:29:21 mydomain qmail-queue-handlers[30393]: to=myaddy@gmail.com
Oct 27 13:29:21 mydomain qmail-queue-handlers[30393]: hook_dir = '/var/qmail//handlers/before-queue'
Oct 27 13:29:21 mydomain qmail-queue-handlers[30393]: recipient[3] = 'myaddy@gmail.com'
Oct 27 13:29:21 mydomain qmail-queue-handlers[30393]: handlers dir = '/var/qmail//handlers/before-queue/recipient/myaddy@gmail.com'
Oct 27 13:29:21 mydomain qmail-queue-handlers[30393]: starter: submitter[30395] exited normally
Oct 27 13:29:21 mydomain qmail: 1256675361.022144 new msg 175875568
Oct 27 13:29:21 mydomain qmail: 1256675361.022918 info msg 175875568: bytes 420 from <anonymous@mydomain.com> qp 30395 uid 48
Oct 27 13:29:21 mydomain qmail: 1256675361.029780 starting delivery 1806: msg 175875568 to remote myaddy@gmail.com
Oct 27 13:29:21 mydomain qmail: 1256675361.029823 status: local 0/10 remote 1/20
Oct 27 13:29:21 mydomain qmail-remote-handlers[30406]: Handlers Filter before-remote for qmail started ...
Oct 27 13:29:21 mydomain qmail-remote-handlers[30406]: from=anonymous@mydomain.com
Oct 27 13:29:21 mydomain qmail-remote-handlers[30406]: to=myaddy@gmail.com
Oct 27 13:29:21 mydomain qmail: 1256675361.696854 delivery 1806: success: 209.85.210.6_accepted_message./Remote_host_said:_250_2.0.0_OK_1256675361_6si1552514yxe.75/
Oct 27 13:29:21 mydomain qmail: 1256675361.6974  

Thanks in advance for your help.

Mark