disable email template for multiple subjects

functions.php

add_filter( 'haet_mail_use_template', 'customize_template_usage', 10, 2 );
function customize_template_usage( $use_template, $mail ){
  if( strpos( $mail['subject'], 'Subject 1' ) !== false
      || strpos( $mail['subject'], 'Subject 2' ) !== false
      || strpos( $mail['subject'], 'Subject 3' ) !== false )
    return false;
  return $use_template;
}

// if you know the exact subject line you can also use == instead of strpos():
add_filter( 'haet_mail_use_template', 'customize_template_usage', 10, 2 );
function customize_template_usage( $use_template, $mail ){
  if( $mail['subject'] == 'Subject 1'
      || $mail['subject'] == 'Subject 2'
      || $mail['subject'] == 'Subject 3' )
    return false;
  return $use_template;
}