How does Exchange Server achieve high availability?

Exchange Server achieves high availability primarily through the use of Database Availability Groups (DAGs). DAGs are a key feature in Exchange Server that allows multiple copies of a mailbox database to be hosted on different servers. This design ensures that if one server experiences a failure, another server with a replicated copy of the database can take over seamlessly, minimizing downtime and ensuring that users continue to have access to their mailboxes.

The architecture of DAGs allows for automatic failover and helps maintain service continuity even during hardware or software failures. With automatic activation of passive database copies, Exchange Server can quickly recover from outages, ensuring a high level of availability for email services.

In contrast, while regular backups are essential for data protection and recovery, they do not directly contribute to high availability since backups typically require downtime to restore data. Limiting access to critical data is more about security than availability. Utilizing virtual server environments can provide benefits like resource management and scaling, but it's the specific mechanism of DAGs that directly addresses the need for high availability in Exchange Server.