One company, as part of its Exchange Server consolidation program, centralized many large Exchange servers into data centers. These servers were performing mailbox, public folder, and routing functions. Mail delivery and routing quickly slowed, and messaging service level agreements (SLAs) weren't being met. To resolve the problem, the company built an Exchange server and configured it to function as a dedicated bridgehead server. This configuration moved to the bridgehead server all the routing functions that the mailbox servers had been performing. The change in server roles immediately resolved mail flow problems.
If a mailbox server is operating under tight SLAs and public folders get a lot of use, a dedicated public folder server can remove additional overhead from the mailbox server. This configuration also lets you configure the mailbox server to function as a dedicated server, with the benefits of faster recovery in the event of a disaster or other mailbox-server failure.