The firewall implemented at your organization might be blocking the email from being delivered. We are looking into improving how our invitation emails are sent.
In the meantime make sure the ResearchPoint email matches the Blackbaud.com username of the new user, and send the ResearchPoint URL (ie. https://login.blackbaudondemand.com/?SiteID=[Enter Site ID]) to the user directly. This will allow them access to ResearchPoint without using the Invitation email.