There are several common deployment scenarios for Symantec Brightmail:
Processing incoming messages to the local message store (ims-ms channel)
Processing messages going out to the Internet (tcp-local channel)
Processing messages coming in from the Internet (tcp-local channel)
Processing messages going to a specific domain (per-domain option)
Processing messages going to specific users (per-user option)
Setting up Brightmail processing as a Class-of-Service Option
If Brightmail implements both spam and virus checking, MTA message throughput can be reduced by as much 50 percent. To keep up with MTA throughput, you might need two Brightmail servers for each MTA.