Microsoft has released Update Rollup 3 for Exchange Server 2010 Service Pack 3.
This update includes a number of fixes that are listed in KB2891587.
Deploying Exchange Server 2010 SP3 Update Rollup 3
The standard order of deployment for Exchange Server updates applies.
- Client Access servers, starting with the internet-facing ones. See this article for how to patch a CAS array.
- Hub Transport and Edge Transport servers
- Mailbox servers. See this article for how to patch a Database Availability Group.
- Unified Messaging servers