Best practices say you should implement LMTP to replace SMTP for message insertion. An LMTP architecture is more efficient for delivering to the back-end Message Store because it:
Reduces the load on the stores. Relays are horizontally scalable while stores are not, thus it is a good practice to make the relays perform as much of the processing as possible.
Reduces IOPS by as much as 30 percent by removing the MTA queues from the stores.
The LDAP infrastructure is often the limiting factor in large messaging deployments.
Reduces the number of message queues.
You need a two-tiered architecture to implement LMTP. See To Configure LMTP Delivery in Sun Java System Messaging Server 6.3 Administration Guide for instructions on configuring LMTP.
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.