In previous versions of Exchange, the information store managed
the databases and the client access protocols such as IMAP4, POP3,
MAPI , and Network News Transfer Protocol (NNTP). In Exchange 2000,
the Internet access protocols have been removed from the store and
instead are managed by Internet Information Services (IIS).
Deploying a front-end/back-end configuration makes it possible to
manage the Internet access protocols on a server that is separate
from the one on which the store and databases run. Essentially, a
bank of protocol servers handle the incoming client connections
while the store servers are dedicated to running the databases.
Benefits of Front-End/Back-End Architecture
The main benefits of a front-end/back-end configuration are a
unified namespace and reduced overhead for Secure Sockets Layer
Unified Namespace. A unified namespace provides easier
administration of multiple IMAP4 servers. For example, if you have
three computers running an IMAP4 virtual server, normally you
divide the user load by configuring certain users to connect to
IMAP4Server1, others to IMAP4Server2, and the rest to IMAP4Server3.
If all IMAP4 servers are part of a front-end/back-end
configuration, a single name provides user access to all IMAP4
servers in your configuration. Clients can be configured to connect
using the name IMAPServer, and software or hardware load balancing
is used to randomly distribute the load among the three IMAP4
servers. Also, when you want to move users' mailboxes from one
server to another, the client does not have to reconfigure the name
of the server they log on to. As your user population grows, you
can add another computer to the front-end bank of servers without
reconfiguring the client.
Reduced overhead for SSL. When connections are made
using SSL, information is encrypted and decrypted, which is very
processor intensive and can affect performance. If your IMAP4
virtual servers are deployed in a front-end/back-end configuration,
the front-end server can process the encryption with the client.
When the front-end server and back-end server communicate, they can
do so without the overhead of SSL encryption. This reduces the load
on the back-end server.