SMTP protocol event sinks are called when SMTP protocol commands (see RFC 822) are received or sent by the SMTP service
Transport Event Sinks
Transport event sinks are fired as a message proceeds through the SMTP transport core. During this process, the message is submitted, categorized, and either delivered locally or relayed to another SMTP service.
Incorrect use of the e-nspect Event Sink Administration Module can seriously damage you SMTP installation.