Mailspring is a mail client that strives to be, "the best new mail client in a decade." Based on the discontinued Nylas Mail, Mailspring retains many of Nylas's unique features while also rewriting substantial portions of the program for increased speed and decreased resource usage. Mailspring includes support for multiple accounts, a unified inbox across all accounts, Gmail-style global search, automatic translation of drafts between languages, and a language-sensitive spell checker. Mailspring comes with a selection of themes to customize the look and feel of the interface. Users may also use the theme starter to build custom themes. The core of Mailspring is open-source and available on GitHub. A professional version is also available for a fee that contains additional features. Mailspring is available for Windows, macOS, and Linux.