In previous versions of Exchange, the information store managed
the databases and 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
are managed by Internet Information Services (IIS) instead.
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 POP3 servers. For
example, if you have three separate computers running a POP3
virtual server, you would normally divide the user load by
configuring certain users to connect to POP3Server1, other users to
connect to POP3Server2, and others to connect to POP3Server3. If
all POP3 servers are part of a front-end/back-end configuration,
there is one name that provides user access to all POP3 servers in
your configuration. Clients can be configured to connect using the
name POP3Server, and software or hardware load balancing is used to
randomly distribute the load to any of the three POP3 servers.
Also, when you want to move a user's mailbox from one server to
another, the client does not have to reconfigure the name of the
server it logs on to. And as your user population grows, you can
add another computer to the front-end bank of servers without
reconfiguring the client.
Reducing the overhead of SSL. When connections are made
using SSL, information is encrypted and decrypted. This encryption
and decryption is processor intensive and can affect performance.
If your POP3 virtual servers are deployed in a front-end/back-end
configuration, the front-end server can process encryption with the
client. Then when the front-end server and back-end server
communicate, they do so without the overhead of SSL encryption.
This reduces the load on the back-end server.