Knowing how to properly pick recipients will help people know what is expected of them, not only in implying whether an email response is expected or not, but also in knowing whether they should act on the message in question or not. This tutorial gives you a quick primer on the three types of email recipients: primary recipients (the "To" email address field), carbon copied ("Cc"), and blind carbon copied ("Bcc"). Since the first two come straight from common practice in real world memos, their intended purpose will already be familiar to many seasoned professionals, so this tutorial will spend more time on blind carbon copies.
Let's start with a remark applies to all types of email recipients: people commonly overlook the fact that they were not the sole recipient of the message you sent. If applicable, make sure that you clearly indicate that multiple parties are concerned, especially since the English pronoun "you" ambiguously refers to singular (one person) and plural (a group of people). Other languages include a (Just as an FYI: like other Germanic languages it partially comes from, Old English used to have "thou" for the singular, and "you" for the plural - now "you" refers to both, and using "thou" in your emails will just make you sound weird!)
Bcc, or Blind Carbon Copy, means by definition that you are hiding something from someone: specifically, you want to keep a third-party in the loop without letting the primary recipient(s) know about it. This extremely convenient feature is supported by nearly all email programs (Microsoft Outlook, Windows Live Mail, etc.) and webmail clients (Hotmail, Yahoo Mail, Gmail, etc.), and can be perceived either as a sneaky tactic, or on the contrary as a tactful gesture.
When sending a mass email or newsletter to a large group of people who may not know each other, err on the side of caution by protecting their privacy: instead of showing their email addresses in the To or Cc fields, add each recipient as blind carbon copied ("Bcc"). The downside of this approach, which will help you determine the best course of action, is that people in a multi-recipient email cannot choose to "Reply to All".