Description of the illustration ''%s''twotier

A connection on the SMTP port of the relay machine is picked up by the dispatcher and handed off to a tcp_smtp_server process. On the message store machine, a connection to the LMTP port is received by the dispatcher and handed off to the lmtp_server process. The LMTP server inserts the message into the user's mailbox. If delivery is successful, the message is dequeued on the relay machine. If unsuccessful, the message remains on the relay machine.