Mail failover in a Domino server cluster

Depending on how your IBM® Domino® server cluster is configured, mail fails over in one of several ways.

If you create replicas of mail databases in a cluster, failover occurs in the following instances:

• When a user tries to open a mail database that is unavailable

  Failover for mail works the same as for any database.

• When a user tries to send a message after the user's mail server has become unavailable

  If a user is composing a message when the mail server becomes unavailable, the user can still send the message. The delivery fails over to another cluster server, where IBM Notes® deposits the message in the outgoing mailbox. Saving the message does not fail over, however, so this message is not saved in the sender's Sent folder.

• When the router tries to deliver mail to a server that is unavailable

  If the server that contains the mail database is unavailable, the router attempts to route the mail to a cluster server that contains a replica of the user's mail database. The router uses the following process to find the correct mail database:

  First, the router checks to see if mail routing failover is enabled for the local server and if the user's mail server is in a cluster. If the local server is in the same cluster and has a replica of the user's mail database, the router delivers the mail to that database. If the local server is in the same cluster but does not have a local replica of the user's mail database, the router uses CLDBDIR.NSF to determine which servers (if any) in the cluster have a replica, and then transfers the mail to one of these servers. If no replica is available in the cluster, or if no server with a replica is available, the router keeps the message and periodically attempts to deliver the mail to the user's mail server without using failover.

  If the local server is not in the same cluster as the user's server, the router identifies another available server in the cluster and transfers the mail to that server. When the mail arrives at the next server, that server repeats the process previously described until the mail is delivered.