Last updated: 4 September 2026

The software

S² Mail is a proprietary desktop email client for Windows, macOS, and Linux. The core client is not open source. You may install and use builds we publish, subject to these terms and any license shown in the application.

No S² account required

You may use the client with mail accounts you already have. Creating an S² account is not required to read or send mail. Paid plans, if offered later, must not prevent access to mail already stored locally if a subscription lapses.

Your mail and providers

You are responsible for complying with the terms of Gmail, Microsoft 365, and any other mail service you connect. S² Mail does not grant you extra rights to those services and is not a party to those contracts.

Acceptable use

Do not reverse engineer the application except where the law allows, do not use it to send unlawful bulk mail, and do not attempt to interfere with update signing or other security controls.

Warranty

Early builds are provided as-is. We work toward production quality, but we do not warrant that a given build is error-free. Keep backups of important mail according to your own policy.

Website

The site at s2mail.app describes the product. Feature lists on the site refer to the current desktop mail client unless they are clearly marked as roadmap items.