IBM Lotus Notes is the client of a collaborative client-server platform. IBM Lotus Domino is the application server. Lotus Notes provides integrated collaboration functionality, including email, calendaring, contacts management, to do tracking, instant messaging, an office productivity suite (IBM Lotus Symphony), and access to other Lotus Domino applications and databases.
Whereas typical email applications are programmed to be an email client, Lotus Notes is an application that is part of an application development platform, where mail is just one of many possible applications. Lotus Notes and Lotus Domino have spawned a great deal of third-party software, including applications, add-ins, add-ons, widgets, plug-ins and more, such as document management systems, discussion forums, and numerous other business applications.
Lotus Notes is commonly deployed as an end-user email client in larger organizations, with IBM claiming a cumulative 145 million licenses sold to date.
When an organization employs a Lotus Domino server, it usually also deploys the supplied Lotus Notes client for accessing the IBM supplied Lotus Notes application for email and calendaring but also to use document management and workflow applications. As Lotus Notes is a runtime environment, and the email and calendaring functions in Lotus Notes are simply an application provided by IBM the administrators are free to develop alternate email and calendaring applications. It is also possible to alter, amend or extend the IBM supplied email and calendaring application.
The Lotus Domino server also supports POP3 and IMAP mail clients, and through an extension product (Domino Access for Microsoft Outlook) supports native access for Microsoft Outlook clients (now with limited support)