Exchange 2010 offers HA using DAG(Database Availability Group). Configuring the DAG alone will not provide HA availability if its not supported by proper planning & design. The different DAG design have been discussed. Take a look at below link to know more. The network latency shouldn’t be more than 25 0ms. You can find more references in the below mentioned articles.
Database Availability Group Design Examples
Exchange 2010 High Availability Misconceptions Addressed
Exchange 2010 Notes from the Field – Multi-Site DAG Design
Understanding Database Availability Groups
Step by Step Create a Database Availability Group (DAG)