Sending Invitation to People for an Event is easy with this script.. download the script from Link
In the address Book
Make a Smart Group to whom you want to send Invitation "SendInviteTo" or use your regular Mailing Group
Make a Group
"Registration Received", -- add the contact that have registered
"Not Interested", "Black List" -- add contact who do not wish to register
"Not Interested", "Black List" -- add contact to whom you do not want to send the invite
"Not for these Company" -- add Contact with the company Name ( just One will do )
in MAIL.APP
Create a new Message with Subject, CC & BCC as require, add body of the message ( do not add Dear or Hi) and then close the message by saving, check in your draft box for the email..