Most MTA channels depend upon a slave or channel program to receive incoming messages. For some transport protocols that are supported by the MTA (like TCP/IP and UUCP), you need to make sure that the transport protocol activates the MTA slave program rather than its standard server. Replacing the native sendmail SMTP server with the MTA SMTP server is performed as a part of the Messaging Server installation.
For the multi-threaded SMTP server, the startup of the SMTP server is controlled by the Dispatcher. If the Dispatcher is configured to use a MIN_PROCS value greater than or equal to one for the SMTP service, then there should always be at least one SMTP server process running (and potentially more, according to the MAX_PROCS value for the SMTP service). The imsimta process command may be used to check for the presence of SMTP server processes. See imsimta process in Sun Java System Messaging Server 6.3 Administration Reference for more information.