I've often see, or have been asked, the question about the difference between the Exchange 2010 SP1 version, available as part of Small Business Server (SBS) 2011, and the “normal” Exchange 2010 SP1 Standard.
The answer to the question is relatively easy, there isn’t.
Alright there is one little difference, if you have configured your Small Business Server with predefined wizards, there are automatically created 3 receive connectors (with 1 that accepts anonymous email from the outside) and 1 send connector. With a normal Exchange 2010 server installation you need to allow anonymous access and create a send connector manually.
Small Business Server 2011 includes the Exchange 2010 SP1 standard version without any limitation. And the Small Business Server Client Access License (CAL) covers the Exchange 2010 CAL.
If you would like to use the so called enterprise functionality like: Custom Retention Policies, Personal Archive, Voicemail, Information Protection and Compliance, Cross Mailbox Search, Legal Hold, Advance Mobile Policies, and Per User/Distribution List Journaling, you need to buy additional the Exchange 2010 Enterprise CAL.
Q. May I use the SBS 2011 CAL Suite to access the Enterprise functionality of Microsoft Exchange Server Enterprise server software?
A. You may use SBS 2011 CAL Suite instead of Exchange Server 2010 Standard CALs to access base functionalities in instances of Exchange Server 2010 Standard or Enterprise in the Windows Small Business 2011 domain. In addition to SBS 2011 CAL Suite, you must acquire Exchange Server 2010 Enterprise CALs to access the following Exchange Server Enterprise functionalities in the Windows Small Business 2011 domain: Custom Retention Policies; Personal Archive; Voicemail; Information Protection and Compliance; Cross Mailbox Search; Legal Hold; Advance Mobile Policies, and Per User/Distribution List Journaling.
Taken from the Small Business Server 2011 Licensing FAQ.
Is there then nothing that cannot be done with Exchange Server in Small Business Server?
Because Small Business Server is based on Windows server 2008 R2 standard, you cannot add the Exchange server to a Database Availability Group (DAG) this feature requires that your operating system is Windows Server 2008 (R2) Enterprise.