I have a pet peeve when it comes to email. When sending a message to more than one person, don’t use the To: field for each and every address. Do you really want to share your addresses with others? Do the people you are emailing to want their address shared with people they may not know? Think about it.
There are exceptions, of course. Emails between committee members working on a project can be included in the To: field, but if you are addressing a specific person and just want the rest to know what is happening, then use To: for the intended person and CC: (carbon copy) to the rest. Doing it that way, there is no confusion as to who needs to answer and who is just being kept up to date.
If you are sending information to clients or vendors, put all addresses in the BCC: (blind carbon copy) field. This will ensure that you are not broadcasting that address list to people who shouldn’t be seeing it. This is something that really bugs me. Do you really want these people to know who else you are mailing? Do they want their addresses shared with others, possible competitors? I have multiple address for multiple purposes, and I don’t like them shared by others.
Oh, and one other thing. If you are forwarding something, please, please, please delete the names of those who sent it and received it before you. I receive jokes from friends that have dozens of those addresses. Not only is it a pain to have to scroll through several screens of names and addresses to get to the body of the message, it’s bad manners. BCC, please!