A. In Exchange Server parlance, a connector server is a server that hosts some number of connectors (such as the Internet Mail Service—IMS, Lotus Notes connectors, or third-party fax or integrated messaging connectors) without hosting any mailboxes or public folders. The idea behind connector servers is that you can centralize some or all of your connectors on a smaller, less powerful server and keep the big iron available for user mailboxes and public folders.
Splitting things up this way has some benefits, apart from the potential performance improvement. One is that providing redundant connectors is much easier. Adding multiple connector servers gives you an easy, cheap route to provide improved redundancy. In many environments, an inexpensive old Pentium box can serve as a backup IMS or Notes connector server. Voila! Load-balancing incoming mail is easy because you can use the free Windows Load Balancing Service available from Microsoft. The normal Exchange Server routing algorithms automatically handle outgoing mail.
Another benefit is that you can reconfigure, update, or move connectors without touching your mailbox servers or disrupting your users’ work. In a perfect world, you'd never need to reboot a server to fix a malfunctioning or stuck connector or apply a hotfix or patch. In reality, though, connectors (whether from Microsoft or third parties) seem to have a higher failure rate than the core components. Putting connectors on separate machines means that when you need to reboot a server, you don't affect mailbox users. Likewise, if you need to add or remove a connector or even swap out an entire server, the impact on users is minimized. Being able to work with your connector servers during the work day is great. Of course, you must have two instances of each type of connector—if you have only one IMS and it's running on a server you reboot, Internet mail will sit until the connector server becomes available again. A final benefit of having a connector server is that in case of emergency, you can always move mailboxes or public folders onto it as a temporary measure.