If you want to have a standard OSC error message like on the create account screen, just add the following 3 lines to catalog/contact_us.php:

After:

$enquiry = tep_db_prepare_input($HTTP_POST_VARS['enquiry']);


Add:

if (tep_validate_email($email_address) == false) {
$error = true;
$messageStack->add('contact', ENTRY_EMAIL_ADDRESS_CHECK_ERROR);
}

Thats it, have fun!

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