Zenoss alerts can be sent to users via email (SMTP) or pager (SNPP.) Many operating systems include an SMTP server (such as Sendmail or Postfix) with their distributions. If your OS does not include a mail server you will need to install one or specify a separate SMTP server in the settings. Many pagers can accept messages via email, but Zenoss also provides the option of sending pages via SNPP if you specify an SNPP server in the settings.