Who's got the Monkey?
Email is one of the primary tools on projects, and is used extensively. As a result, personnel on the project may receive literally hundreds of project emails a day each, particularly the Project Manager. All of these emails are important to the project, however we all need to be careful to ensure that messages are targeted and tagged appropriately so that:
(a) the right people are looking at the messages
Sometimes, you will need to have more than one "Monkey", where decisions will require input from a select group. In this case, by all means include them all in the TO: line - but make it clear what is expected of them in the email, and by when. And if different people have different tasks, highlight them early in the email, ideally in the first page, so they know to read on further. Don't leave the assignment "hooks" until the end. Most people will skim and stop reading before they get there.
(4) One thread, one subject, one topic. Most mail programs have threading capability, and it makes it much easier for tracking through old emails on a topic if the subject actually relates to the content - and the subject line is maintained throughout the thread. This simple convention can literally save hours "trying to find that email back from April - or was it February?"
And it goes without saying - do not respond to topic A under Subject B. Start a new thread or respond to the correct email. Keep the threads clean, and in context.