If you are an event organiser sending emails to many recipients it is a good idea to put the destination email addresses the BCC (Blind Carbon Copy) field, rather than the TO field. This will prevent recipients from being able to see everyone else's email address, which some people might object to.
It's very easy to do once you know how, no more difficult than sending a normal email.
Here is some links which tells you how to do it using various types of email software:
