The Mail Service Layer
This layer handles the connectivity of the Exchange server to different hosts in the environment.
This layer also monitors the traffic on the protocols that have been described below.
The Internet Messaging Access Protocol version 4.0 (IMAP4) works like POP3. This protocol enables clients to access and manipulate messages stored within their mailboxes. Unlike POP3, IMAP4 allows a user to access multiple e-mail folders, search through a mailbox, and maintain read and unread message flags. In addition, a user can download an entire message or a portion of a message, such as an attachment. The traffic statistics pertaining to the use of POP3 and IMAP4 protocols via an Exchange server are monitored using eG Enterprise's XchgMailRetrieval test (see Figure 4). SMTP is the primary protocol that is used by mail clients to send email messages to a mail server. Moreover, SMTP is also the main mechanism used by mail servers to exchange emails between themselves. eG Enterprise's XchgMailTransfer test (not shown in Figure 4) is used to monitor SMTP protocol usage statistics for an Exchange server.