You must follow the configurations that are recommended for Exchange Server 2010 on Database Availability Group (DAG) setup.
To configure Symantec Mail Security for Exchange 2010 on DAG setup
In the console on the toolbar, click Assets.
In the Asset Management window, under Tasks, click New group.
Create a new group for exchange 2010 DAG servers.
Create separate groups for each DAG if there are multiple DAG groups. Set up a quarantine server on each DAG group from the console so that the quarantine data is available if any DAG server is unavailable.
Click Add server(s) and add all DAG member servers to the new group.
Create and apply the same security policies to every server in the group to ensure that all the mailboxes have the same Mail Security settings if a database failover occurs.