Red Hat Enterprise Linux 5 Administration Unleashed

CHAPTER 18Setting Up an EmailServer with SendmailIN THIS CHAPTER. Understanding Email Concepts. Configuring Sendmail. Using POP and IMAP. Logging Sendmail Connections. Allowing Email ConnectionsIn a corporate environment, email is an essential componentto the work day. Email is used to schedule and remindemployees of meetings, communicate with both internalemployees and external customers, and enable remoteemployees to participate in company discussions; it has eventaken the place of water cooler talk for some employees.The first part of this chapter outlines how an emailmessage reaches its destination email server. The secondpart of the chapter explains how to set up Red HatEnterprise Linux to send and receive email with Sendmail.Finally, users must retrieve email off an email server froman email client using a protocol such as POP or IMAP.Configuring the email server to allow POP and IMAPconnections is discussed in the last part of this chapter.Understanding Email ConceptsWhen a person wants to send an email to someone else onthe Internet, she opens an email client, which is also calleda Mail User Agent (MUA), such as Evolution or Thunderbird.Instead of using a standalone email client, you can also usea web browser to access a web-based email client or evenan application on a portable Internet device such as a cellphone or PDA.After you send an email, the email is formatted into a standardformat so that all the other email servers on theInternet can read it.