Introduction to Virtual Servers

Just as they were in Exchange 2000 Server on Windows 2000 Server, Exchange Server 2003 and IIS 6.0 are tightly integrated to provide a robust messaging solution that is capable of supporting multiple messaging protocols. Exchange Server 2003 supports messaging using the following protocols:

• Post Office Protocol version 3 (POP3) using port 110 default and port 995 by default for POP3 over SSL (Secure Sockets Layer). POP3 is a standard, and fairly limited, email retrieval protocol that remote users can use to access their Exchange mailboxes. Outlook and Outlook Express support POP3.

• Internet Message Access Protocol version 4 (IMAP4) using port 143 by default and port 993 for IMAP4 over SSL. IMAP4 is a newer, and more complex, email retrieval protocol that supports a more advanced feature set than POP3. IMAP4 allows you to organize messages by creating folders on the server and also allows for message preview by only downloading message headers instead of the entire message. Outlook and Outlook Express support IMAP4.

• Simple Mail Transfer Protocol (SMTP) using port 25 by default and port 25 by default for SMTP over SSL. SMTP is used to send outgoing messages to an Exchange server and also to send messages from one server to another en route to their final destination. Outlook and Outlook Express support SMTP.

• Hypertext Transfer Protocol (HTTP) using port 80 by default and port 443 by default for HTTP over SSL. HTTP is primarily used by Outlook Web Access (OWA) clients to access their Exchange mailboxes and calendars at the URL http://servername/exchange/. All mailbox items are referenced by complete URLs, so the inbox can be accessed at http://servername/exchange/mailbox/inbox

• Network News Transfer Protocol (NNTP) using port 119 by default and port 563 by default for NNTP over SSL. NNTP is used by newsreaders to access public folders. Outlook Express supports NNTP.

Recall that because each of these protocols uses its own default port, you only need one IP address to house multiple protocols on a single server. The true magic behind this is the virtual server. By default, Exchange creates a virtual server for each protocol listed previously, as shown in Figure 6.15.

Figure 6.15. Exchange creates multiple virtual servers to facilitate mail transfer.

In a default Exchange organization, only the HTTP and SMTP virtual servers are operational. You can opt to enable the POP3, NNTP, and IMAP4 virtual servers as needed. Alternatively, you might want to remove some virtual servers from one server and re-create them on a different server in an effort to load-balance client access to your Exchange servers.

In larger environments, you might consider placing one protocol on one physical server, further reducing server loading. Alternatively, you might need to create multiple virtual servers for SMTP or NNTP to provide both load balancing and redundancy for client access to these services.