leadin custom welcome message

functions.php

function cv_leadin_subscribe_email( $fields ){
  $body = file_get_contents( get_stylesheet_directory() . '/leadin/email.html' );
  $replacements = array();
  foreach ( $fields as $field ) {
    $brace_label = "{" . ucwords( $field['label'] ) . "}";
    $replacements[$brace_label] = $field['value'];
  }

  $body = strtr($body, $replacements);
  return $body;
}