It's only good manners to use BCC (blind carbon copy) rather than CC (carbon copy) when sending out an email to a group of people; not everyone wants their email address shared with all your other friends.

If you're worried about a mass email landing your friends' or colleagues' addresses into spam boxes, limit the number BCC'd on each email to around 20 people. Some servers will refuse to accept larger numbers of names with the same server - for example, some government servers; if you want to email all the TDs in the Dail, do it in groups.