ParaInvite uses Joomla's mail API to send out emails. If your invites are not sent, try doing the following:

• Check your server's mail queue and see if the emails are properly sent
• Ensure your host does not have a email limit (some hosts restrict their customers to send out a fixed number of emails a day)
• Ensure that your server's MX record is not blacklisted by webmails (eg Hotmail, Gmail etc)
• For best results, use SMTP for mail (set in Joomla configuration)