Basic spam protection for Gravity Forms

functions.php

<?php

// simple spam protection - drop any submissions where email is in a blacklist
// note: this function assumes that form has honeypot field enabled.
function pre_validation_handler( $form ) {
  
  // blacklist is an array of bad email addresses or spam phrases
  // for now, just a single (real) spammer
  $blacklist = [ 'atouchofawesomeness@gmail.com' ];
  
  // loop thru fields looking for spammers
  foreach( $form['fields'] as &$field ) {

    // get the submitted value for this field
    $value = RGFormsModel::get_field_value( $field );

    // check if value in array
    // note: this could be enchanced with a regex check or similar
    if ( in_array( $value, $blacklist ) ) {

      // honeypot is not a field at this point in processing, thus we cannot get ID
      // so lets just do what GF does..
      $honeypot_field_id = GFFormDisplay::get_max_field_id( $form ) + 1;
      // then we set the honeypot value
      $_POST['input_' . $honeypot_field_id] = 'blacklisted';
      // and let GF do the rest
      return $form;

    }
  
  }
  
  return $form;
}
add_action( 'gform_pre_validation', 'pre_validation_handler' );