There are many alternatives to sup for Linux if you are looking for a replacement. The best Linux alternative is Thunderbird, which is both free and Open Source. If that doesn't suit you, our users have ranked more than 25 alternatives to sup and many of them are available for Linux so hopefully you can find a suitable replacement. Other interesting Linux alternatives to sup are Evolution, Zoho Mail, Geary and Claws Mail.
Cross-platform email client supporting multiple identities, chat, and strong filtering. Extend functionality with add-ons like RSS/Atom feed readers and PGP support.
Evolution is a personal information management application that provides integrated mail, calendaring, address book and task list functionality.
Zoho Mail is a secure, encrypted, and enterprise-ready email solution, a suite of apps tailor-made for your organization's needs.
Geary is an email application built around conversations, for the GNOME 3 desktop.
Email and news client on GTK+ foundation featuring quick performance, extensible plugins, secure protocols, advanced filtering, strong folder and contact management, lightweight design, powerful search, customizable interface, multi-language support, and encryption.
Modern open-source email client supporting unified inbox, IMAP/SMTP, Gmail and Outlook with OAuth2, conversation threading, rich text TipTap composing, CardDAV contact sync, tracking removal, dark mode, color themes, vim-style shortcuts, and a detachable window.
Mutt is a small but very powerful text-based mail client for Unix operating systems. Some of its features are: color support, message threading, MIME support (including RFC2047 support for encoded headers), PGP/MIME (RFC2015), various features to support mailing lists, including...
Sylpheed is a simple, lightweight but featureful, and easy-to-use e-mail client (mailer, MUA).
The free Zimbra Desktop client allows you to meld the online and offline worlds – storing and synching your email, calendar, contacts, files and documents in the cloud, yet having them locally accessible when on the road.
KMail is the email component of Kontact, the integrated personal information manager of KDE. Kontact is a personal information manager and groupware software suite for KDE. It supports calendars, contacts, notes, to-do lists, news, and email.
aerc is an email client that runs in your terminal. It's highly efficient and extensible, perfect for the discerning hacker.
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This is actually the only GUI MUA I can tolerate, and it does everything I need. A nice bonus is the ManageSieve plugin, to handle filters on the mail server.