You should not process information about people that they are not aware of you having – for example lists that you have found or been given by anyone other than the people themselves. You cannot assume that if data exists it is with the people’s knowledge and consent.
You should not use data in any fashion that would not be in line with the expectations of the person whose data it is – if you have been given an email address to send an invitation to a specific event then it should not be assumed that the person would welcome other messages. It certainly should not be passed on to any other party – even in relation to the event itself – without explicit permission.