Email script error message RCPT

Code:
-- send an e-mail
function mail(to, subject, message)
  -- make sure these settings are correct
  local settings = {
    -- "from" field, only e-mail must be specified here
    from = 'xxxxx',
    -- smtp username
    user = 'xxxxx',
    -- smtp password
    password = 'xxxxx',
    -- smtp server
    server = 'smtp01.binero.se',
    -- smtp server port
    port = 465,
    -- enable tls, required for gmail smtp
    secure = 'sslv23',
  }

  local smtp = require('socket.smtp')

  if type(to) ~= 'table' then
    to = { to }
  end

  for index, email in ipairs(to) do
    to[ index ] = '<' .. tostring(email) .. '>'
  end

  -- fixup from field
  local from = '<' .. tostring(settings.from) .. '>'

  -- message headers and body
  settings.source = smtp.message({
    headers = {
      to = table.concat(to, ', '),
      subject = subject,
      ['From'] = from,
      ['Content-type'] = 'text/html; charset=utf-8',
    },
    body = message
  })

  settings.from = from
  settings.rcpt = to

  return smtp.send(settings)
end