You can invite new attendees or remind participants for your event or other campaigns by sending them an email from your campaign's admin area at Manage Event Campaign -> Emails.
You can either select all invitees or select a subset using tags or city or zip code or other filtering criteria to segment from your contacts database to send invitations to your event/ campaign.
You can also schedule and send reminders to participants to your event.
Note that you can track the emails by the number of opens, clicks, and CTA (ticket purchase, poll participation, etc.) sent.