Which of the following should be implemented to ensure email continuity is not disrupted if one of multiple datacenters experiences an outage?

Geo-clustering links application clusters across geographic sites and requires active cluster synchronization overhead, whereas the question targets a simpler path-redundancy mechanism to handle datacenter outages.

Offsite backup preserves copies of email data for disaster recovery purposes but does not maintain live service availability during an active datacenter outage.

Local load balancing distributes traffic among servers within a single datacenter only and cannot redirect email traffic to a different datacenter when an outage occurs.

Multipathing establishes multiple independent physical or logical paths between clients and email servers across datacenters, so that if one datacenter's path or connection fails, traffic automatically reroutes over a surviving path. This path-level redundancy ensures continuous email availability without requiring manual failover actions. Because the email service is reachable through an alternate route, continuity is preserved even during a full datacenter outage.