Contact Form Domain Blacklists (using java, html or php)

I'm using HTML contact forms on a business site to post lead information to Salesforce. We're using auto-responders to deliver key information to people who complete a form asking for additional information. The goal is to reject forms that are submitted by competitors. It doesn't need to be bullet proof; the main idea is to reject and form that has an email address associat开发者_如何转开发ed with a competitor's domain.

Can anyone help? Thanks!

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Try making an array of all emailadresses like this

$emails = array($this->getEmails());
if(is_array($emails) && in_array($_POST["emailadres"],$emails))
{
// if we are here then it is not blacklisted
return true; // or whatever 
}
else
{
return false; // eighter it was a blacklisted email or the $emails wasnt an array  
}

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Are you programming the form? If so, input validation? Not sure of the question here, but sounds like simple input validation.