Need help troubleshooting source of spam flagging for email being sent through VB.
 

Here's the problem. In the 'Contact Us' form* I created a special option with a designated email address associated with it. This email address is setup with an auto-responder through cPanel at my hosting company that spits out the information being requested when someone selects this radio button option in using the 'sendmessage.php' feature.

For some strange reason* the emails that get sent out by the auto-responder are being flagged as spam always by yahoo* some of the time by gmail* but others like hotmail allow them through. And yes* I am using all the email authentication features available: DomainKeys & SPF enabled* as well as reverse DNS setup.

Is it possible that vbulletin is somehow creating something as a result of the mail routing that causes aggressive spam filters to identify it as spam?

I'm wondering how best to isolate the cause. One thought is to create my own form on a separate webpage of my domain so that info requests go straight to my email accounts at my domain* thus bypassing vbulletin.

Anybody have any ideas or suggestions?

TIA