HCL Notes provides business collaboration functions, such as email, calendars, to-do lists, contact management, discussion forums, file sharing, websites, instant messaging, blogs, document libraries, user directories, and custom applications.

Domino provides email, calendars, instant messaging (with additional HCLSoftware voice- and video-conferencing and web-collaboration), discussions/forums, blogs, and an inbuilt personnel/user directory.

Features include group calendars and schedules, SMTP/MIME-based email, NNTP-based news support, and automatic HTML conversion of all documents by the Domino HTTP task.

In addition to its role as a groupware system (email, calendaring, shared documents and discussions), HCL Notes and Domino can also construct "workflow"-type applications, particularly those which require approval processes and routing of data.

Domino software can run on Windows, Unix, AIX, and IBM mid-range systems and can scale to tens of thousands of users per server.

Usually the latest server operating system is only officially supported by a version of HCL Domino that is released at about the same time as that OS.

Replication between a Notes client and Domino server can run automatically according to a schedule, or manually in response to a user or programmatic request.

Lotus Notes was the first widely adopted software product to use public key cryptography for client–server and server–server authentication and for encryption of data.

Some governments objected to being put at a disadvantage to the NSA, and as a result Lotus continued to support the 40-bit version for export to those countries.

Notes and Domino also uses a code-signature framework that controls the security context, runtime, and rights of custom code developed and introduced into the environment.

This sets it apart from its major commercial competitors, such as Microsoft Exchange or Novell GroupWise, which are purpose-built applications for mail and calendaring that offer APIs for extensibility.

Notes is a document-oriented database (document-based, schema-less, loosely structured) with support for rich content and powerful indexing facilities.

This means that the design of the database can replicate to users' desktops just like the data itself, making it extremely easy to deploy updated applications.

Traditional database developers used to working with rigidly enforced schemas, on the other hand, may consider the power of this feature to be a double-edged sword.

While LotusScript remains a primary tool in developing applications for the Lotus Notes client, Java and JavaScript are the primary tools for server-based processing, developing applications for browser access, and allowing browsers to emulate the functionality of the IBM Notes client.

External to the Notes application, HCL provides toolkits in C, C++, and Java to connect to the Domino database and perform a wide variety of tasks.

Document-oriented databases such as Notes allow multiple values in items (fields), do not require a schema, come with built-in document-level access control, and store rich text data.

There are several spam filtering programs available (including IBM Lotus Protector), and a rules engine allowing user-defined mail processing to be performed by the server.

The Notes client was also designed to run on multiple platforms including Windows, OS/2, classic Mac OS, SCO Open Desktop UNIX, and Linux.

Furthermore, these differences have often remained in the product to retain backward compatibility with earlier releases, instead of conforming to updated Windows UI standards.

This new user experience builds on Notes 6.5 (released in 2003), which upgraded the email client, previously regarded by many as the product's Achilles heel.

Features added at that time included: Publications such as The Guardian in 2006 have criticized earlier versions of Lotus Notes for having an "unintuitive [user] interface" and cite widespread dissatisfaction with the usability of the client software.

The Guardian indicated that Notes has not necessarily suffered as a result of this dissatisfaction due to the fact that "the people who choose [enterprise software] tend not to be the ones who use it.

"[22] Earlier versions of Notes have also been criticized for violating an important usability best practice that suggests a consistent UI is often better than custom alternative.

Old versions did not support proportional scrollbars (which give the user an idea of how long the document is, relative to the portion being viewed).

One example that was corrected in Release 8.5: In earlier versions the out-of-office agent needed to be manually enabled when leaving and disabled when coming back, even if start and end date have been set.

So, depending on system settings, users will have no choice in return receipts going back to spammers or other senders of unwanted e-mail.

Domino 12.0.2 supports two new federated-identity login techniques that leverage signed JSON Web Tokens (JWTs) acquired from OpenID Connect (OIDC) providers.

[91] Despite repeated predictions of the decline or impending demise of IBM Notes and Domino, such as Forbes magazine's 1998 "The decline and fall of Lotus",[92] the installed base of Lotus Notes has increased from an estimated 42 million seats in September 1998 [citation needed] to approximately 140 million cumulative licenses sold through 2008.

IBM's development and support team responsible for these products are moving to HCL, however, the marketing, and sales continue to be IBM-led.