These are the various notification methods used in SMEX:

Collaboration Data Objects (CDO)

CDO is a Component Object Model (COM) module provided by Windows. It has an API set that can be used by applications that create and send messages using SMTP/NNTP protocol or by ASP applications providing messaging capabilities. CDO simplifies the writing of programs that manipulate Internet messages.

Collaboration Data Objects for Exchange (CDOEX)

CDOEX is a superset of CDO. It provides interfaces that can be used to access and manage most types of information in the Microsoft Exchange store database. It can be used in applications that support sending/processing of emails and managing contacts and calendar appointments. Unlike CDO, applications using CDOEX can only be executed on a server which has Exchange installed. Consequently, since CDOEX leverages Exchange, it requires a mailbox to be used for sending out messages.

Exchange Web Services (EWS)

EWS is the Microsoft-recommended API set for Microsoft Exchange programming. It provides an integrated access to Exchange Server resources while leveraging logic that is compatible with Microsoft Outlook. It has been created to replace CDOEX, MAPI and other older interfaces used to interact and manage different Exchange data. One of the preliminary steps in gaining access to Exchange via EWS is to communicate with an Exchange Client Access Server (CAS).