how to alter notification email in search api saved search module. I want to add more details about the search
hook_mail_alter is your best friend, just keep in mind this hook fired on all emails so make sure you check if your are targeting the search-API emails. Here is a snippet of code copied from the mail_example module:

function email_example_mail_alter(&amp;$message) {
  // For the purpose of this example, modify all the outgoing messages and
  // attach a site signature. The signature will be translated to the language
  // in which message was built.
  $options = array(
    'langcode' =&gt; $message['language']-&gt;language,
  );

  $signature = t("\n--\nMail altered by email_example module.", array(), $options);
  if (is_array($message['body'])) {
    $message['body'][] = $signature;
  }
  else {
    // Some modules use the body as a string, erroneously.
    $message['body'] .= $signature;
  }
}