As of the Messaging Server 6.0 release, you can configure LMTP for delivery to the Message Store in a multi-tiered deployment. In these scenarios, where you are using inbound relays and back-end Message Stores, the relays become responsible for address expansion and delivery methods such as autoreply and forwarding and also for mailing list expansion.
Delivery to the back-end stores historically has been over SMTP, which requires the back-end system to look up the recipient addresses in the LDAP directory again, thereby engaging the full machinery of the MTA. For speed and efficiency, the MTA can use LMTP rather than SMTP to deliver messages to the back-end store. See Chapter 16, LMTP Delivery, in Sun Java System Messaging Server 6.3 Administration Guide for more information.
By design, LMTP is intended for use in multi-tier deployments. It is not possible to use LMTP with single-system deployments. Also, the Messaging Server’s LMTP service as implemented is not designed to work with other LMTP servers or other LMTP clients.