Which Cisco voice messaging components support active-passive redundancy?

Cisco Unity
Cisco Unity supports two categories of redundancy. The first one is referred to simply as Unity Failover (local messaging failover), and it provides system malfunction failover. The second category is referred to as Standby Redundancy, and it provides disaster-recovery across geographic locations. See the Cisco Unity Design Guide for a comparison of Cisco Unity Failover and Standby Redundancy.

Cisco Unity failover consists of two servers, a primary and a secondary, configured as an active/passive redundant pair of servers, where the primary server is active and taking calls while the secondary is inactive and not taking calls. Any changes to subscriber or configuration data on the primary server are automatically replicated to the secondary server. If the primary server stops functioning for some reason, the secondary server automatically becomes the active server and starts taking calls while the primary server temporarily becomes inactive.

https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/srnd/8x/uc8x/vmessage.html