The following tables compare general and technical features of notable non-web-based email client programs.
Basic general information about the clients: creator/company, O/S, license, and interface.
A brief digest of the release histories.
The operating systems on which the clients can run natively (without emulation).
What email and related protocols and standards are supported by each client.
Information on what features each of the clients support.
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.
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.