Clustering support can be based on the Internal Distributed User Database (introduced in version 8.2 and currently the recommended way) or LDAP Integration and enables routing and authentication for the SMTP Incoming, WebMail, POP3 and IMAP proxy services. This feature enables you to spread mailboxes on several Axigen servers and have a separate machine that routes POP3/IMAP connections to the appropriate mailbox server.
Axigen Cluster is a type of Load Balancing Cluster and this functionality is used when deploying a Multi Tier Architecture. See our Documentation section: Highly Available, Scalable, Multi-tier Solution Architecture:
In this type of architecture, the job of the Front End Nodes is to perform routing and authentication.
The Routing function has the task to ensure that messages and connections are routed to the appropriate node (depending on the account for which a request is being performed) in the back-end tier.
The Authentication function has the task of performing authentication on the Front End nodes in order to offload this task from the backend nodes, to act as a first layer of validation and makes sure that only valid and authenticated connections are sent to the back-end tier.