[This is preliminary documentation and subject to change.]
SMTP protocol and transport events provide a means by which you can enhance and extend the functionality of the SMTP service. For example, through SMTP service events, you can create high performance applications that do the following:
Alter or extend the protocol commands supported by the service.
Examine a message for incorrectly formatted or unsafe content, and block transmission or deliver of the message.
Provide custom logic used to categorize the message, including resolving relay or delivery locations, and expansion of distribution lists.
Install a custom store for local message delivery other than the default SMTP service drop directory.
Enhance or extend the routing logic of the service by providing extensions that use custom logic to determine where the SMTP service should connect to relay a message not categorized as a message for local delivery.