Exchange Server Mailbox Services

The Exchange server product has slowly evolved to be much more than simple e-mail services; however, the heart of the product still lives on in the Mailbox role. Microsoft's original mail product, Microsoft Mail, was little more than message items stored on disk and some external applications that acted as message transport agents (MTAs) that were used to move mail around. As electronic messaging became more important to businesses, it was clear that the architecture of Microsoft Mail would not scale to meet growing business needs; it was then replaced with the Exchange Server product. Version 4.0 was the first version of Exchange Server, coming to the market in 1996 to provide improved scalability and improve the connectivity of the e-mail system to other systems.

Exchange Server 4.0 did provide a more scalable product, with a unified address book and a way to interface with a variety of e-mail systems. As Exchange Server 5.0 and Exchange Server 5.5 came to market, additional connectors were made available to embrace emerging Internet standards like SMTP. Also added in Exchange Server 5.5 was a Web-based client originally named the Exchange Web Client and then renamed Outlook Web Access (now renamed Outlook Web App in Exchange Server 2010).

With the introduction of Exchange 2000 Server, Outlook Web Access also ran not only on the same server, but the core functionality ran in the Information Store (store.exe), which was the same process that handled the database functionality. Exchange 2000 Server also introduced the streaming database file (STM) to store the content of messages that were not in native MAPI format. When these messages were accessed by a MAPI client, the data would be promoted into the ESE Exchange database; however, if the message was accessed with an IMAP or POP3 client no conversion would happen. The intent was to reduce the amount of conversions that needed to happen and thereby reduce the overall resources required on the Exchange Server. The streaming database file was discontinued starting with Exchange Server 2007.

Beginning with Exchange Server 2007, the development team began peeling out many of these functions from the database to reduce the bloat and sensitivity to any code changes. For example, in Exchange 2007 the Outlook Web Access (OWA) was completely rewritten. OWA no longer used the Information Store to render the HTML for OWA. Also, the Exchange Server 2007 introduced server roles, allowing separation of functionality onto different servers, only needing to run the required roles on specific servers. Again in Exchange 2010 additional functionality was removed from the database and moved to other roles. For example, in Exchange Server 2010, MAPI-based client connectivity has been moved from the Mailbox role to the Client Access Server role. Having fewer non-core functions running within the information store process has improved performance and stability and added in additional high-availability functionality.