You should be able to do this with the standard email delivery channel that ships with PI Notifications. Please consult PI Notifications User guide at vCampus Library. Here's a quote:
You might need to edit the SMTP Server Configuration restart service. PI Notifications Service uses SMTP to send emails. The service requires that it can connect and use a SMTP Server. Two common SMTP servers are the IIS SMTP Virtual Server and Microsoft Exchange’s default SMTP Server. See the information on configuring the email delivery channel in PI System Notifications help or the PI Notifications User Guide.