Question : 550 Backscatter Protection detected an invalid or expired email address

We have a website, smartdesigns.com that has multiple forms.
One of the forms is for clients to request support and info regarding our products.
As of this morning we did not reveive and new leads or support requests.
Thinking it was a form online I decided to fill one out and check our mail system to
see if the emails were coming through. I saw the email come in and noticed the message
"550 Backscatter Protection detected an invalid or expired email address" then the
email never come into our general inbox. If we send an email to the account from an email client it will accept the email and send an autoresponse. I decided to disable the setting for
backscatter to see what happens. The mail system now receives the email and places
it in the proper inbox but fails to send an auto responder. Nothing has changed.

As of right now I am not sure if the issue is related to the forms on our site or the mail system. You will notice that once the form is filled out and sent it goes to a box on our webhost then from there it sends the mail to the inbox that the form is associated with. Posted below is a sample of why I think its having a problem:

250 mail.smartdesigns.com Hello outbound-mail-146.bluehost.com, pleased to meet you
<-- MAIL FROM:<>
Performing SPF lookup (outbound-mail-146.bluehost.com / 67.222.38.36)
* Result: none; no SPF record in DNS
---- End SPF results

--> 250 <>, Sender ok -------------------- This is the puzzling part, there is suppose to be an address here in between <>. This is what I believe triggers the backscatter to reject the email. Also the reason why the auto responders are not working...

<-- RCPT TO:om>
Performing Backscatter Protection...

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Session 392; child 1; thread 4100
Accepting SMTP connection from [67.222.39.24:41789]
Performing PTR lookup (24.39.222.67.IN-ADDR.ARPA)
*  D=24.39.222.67.IN-ADDR.ARPA TTL=(1411) PTR=[outbound-mail-134.bluehost.com]
*  Gathering A records...
*  D=outbound-mail-134.bluehost.com TTL=(211) A=[67.222.39.24]
 ---- End PTR results
 --> 220 mail.smartdesigns.com ESMTP MDaemon 9.6.6; Tue, 25 Aug 2009 14:50:51 -0700
 <-- HELO outbound-mail-134.bluehost.com
 Performing IP lookup (outbound-mail-134.bluehost.com)
 *  D=outbound-mail-134.bluehost.com TTL=(211) A=[67.222.39.24]
 ---- End IP lookup results
EHLO/HELO response delayed 1 seconds
 --> 250 mail.smartdesigns.com Hello outbound-mail-134.bluehost.com, pleased to meet you
 <-- MAIL FROM:<>
 Performing SPF lookup (outbound-mail-134.bluehost.com / 67.222.39.24)
 *  Result: none; no SPF record in DNS
 ---- End SPF results
 --> 250 <>, Sender ok
<-- RCPT TO:
 Performing Backscatter Protection...
*  Address: [email protected]
*  Verifier: 
*  Result: fail
*  Reject: Yes
 --- End Backscatter Protection
 --> 550 Backscatter Protection detected an invalid or expired email address
 <-- QUIT
--> 221 See ya in cyberspace
 SMTP session terminated (Bytes in/out: 93/283)

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Answer : 550 Backscatter Protection detected an invalid or expired email address

So, at least, If you change
$mailheaders = 'From: <'.$_POST['email'].'>' . "\r\n";
$mailheaders .= "Reply-To: $_POST[email] \n";
by
$mailheaders = "From: [email protected]\r\nReply-To: [email protected]";
you will be sure the from field will be filled, and if somebody dont fill the mail email field you will receive the message anyway.