The following tables compare general and technical features of notable email client programs.

General

Basic general information about the clients: creator/company, O/S, license, and interface. {{legend|#f4e3ff| No longer in active development}}

Release history

A brief digest of the release histories.

Operating system support

The operating systems on which the clients can run natively (without emulation).

Protocol support

Communication and access protocol support

What email and related protocols and standards are supported by each client.

Integration protocol support

Authentication support

SSL and TLS support

Features

Information on what features each of the clients support.

General features

For all of these clients, the concept of "HTML support" does not mean that they can process the full range of HTML that a web browser can handle. Almost all email readers limit HTML features, either for security reasons, or because of the nature of the interface. CSS and JavaScript can be especially problematic.

Messages features

Database, folders and customization

Templates, scripts and programming languages

Internationalization

The Bat! supports Email Address Internationalization (EAI). As of October 2016, email clients supporting SMTPUTF8 included Outlook 2016, mail for iOS, and mail for Android.