KB 982639 lists all the fixes included in this rollup. Here are some of the product improvements and critical bug fixes we'd like to call out starting with 5 improvements we made to prevent crashes in very unique scenarios.
KB 980852 The RpcClientAccess process on an Exchange Server 2010 server crashes when you access a mailbox by using a MAPI application
KB 979801 An error message is generated in Exchange Server 2010 when you use Exchange Troubleshooting Assistant
KB 980364 The Exchange Transport service on an Exchange Server 2010 server crashes when a certain message is processed
KB 980353 A MAPI application that is used to access Exchange Server 2010 mailboxes crashes when the application accesses an address book
KB 979790 An IMAP4 client crashes when accessing an Exchange Server 2010 mailbox
We corrected a few replication issues some of you encountered.
KB 980149 The Add-MailboxDatabaseCopy command fails when it is used to add a database copy to a Database Availability Group in an Exchange Server 2010 environment
KB 981961 Event ID 4033 is logged and the Free/Busy replication from an Exchange Server 2003 server to an Exchange Server 2010 server fails
KB 979921 You cannot replicate a public folder from one Microsoft Exchange Server 2010 server to another, and Event ID 3079 is logged on the target server
One unique thing added was an ability for an administrator to adjust filtering of XML attachments so an OWA user can save them. Some customers were facing a compliance versus level of security tradeoff. See more about configuring this option in KB 983200, which discusses adding administrator control over attachment stripping. We also included at least eight other fixes that some of you requested in this release which we already had worked on for a service pack but are able to deliver to you sooner.
KB 982639 has more details about this release and a complete list of all fixes included in this worthwhile rollup.
For those of you running Forefront, be sure you perform these important steps from the command line in the Forefront directory before and after this rollup's installation process. Without these steps, Exchange services for Information Store and Transport will not start back up. You will need to disable ForeFront via "fscutility /disable" before installing the patch and then re-enable after the patch by running "fscutility /enable" to start it up again post installation.
Questions / discussions of the Update Rollup and issues