Opera Mail is described as 'Powerfully organizes, indexes, and sorts your messages' and is a very popular Email Client in the office & productivity category. There are more than 25 alternatives to Opera Mail for a variety of platforms, including Windows, Android, Mac, Linux and Android Tablet apps. The best Opera Mail alternative is Thunderbird, which is both free and Open Source. Other great apps like Opera Mail are K-9 Mail, Evolution, Microsoft Outlook and FairEmail.
Cross-platform email client supporting multiple identities, chat, and strong filtering. Extend functionality with add-ons like RSS/Atom feed readers and PGP support.
K-9 is an open source email client for Android with multi-folder sync, email signatures, Bcc-to-self, return-address configuration, keyboard shortcuts, Exchange Support, message flagging, IMAP deletes, saving attachments, configurable notifications and more.
Evolution is a personal information management application that provides integrated mail, calendaring, address book and task list functionality.
Streamline emails, calendars, contacts, and task management with a smart inbox prioritizing critical messages. Includes calendar scheduling, third-party app integration like Facebook, Dropbox, and Trello, and support for Microsoft Exchange, Outlook.com, and Gmail, ensuring efficient task and email handling.
Open-source, privacy-focused email client offering features such as encryption via OpenPGP and S/MIME, unlimited accounts, a unified inbox, customizable settings, and reformatted emails to prevent phishing. Supports two-way synchronization and provides Pro features for additional customization.
eM Client is a full featured e-mail client with a modern and easy to use interface. eM Client also offers calendar, tasks, contacts, notes and chat.
E-mail app with all the great features: swipes (long/short), snooze, add (multiple) attachments from the cloud, support for various e-mail services and more.
Access, view and manage messages from all your email accounts in one place. Categorize your messages into easy to browse categories. Catch up on email easily with Apple Intelligence powered Priority Messages and summarizations.
Boost your productivity and send better email with Mailspring, a beautiful, fast email client for Mac, Windows, and Linux. Mailspring is free to use and an optional pro version adds read receipts, send later, reminders and more.
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.
Geary is an email application built around conversations, for the GNOME 3 desktop.
Sylpheed is a simple, lightweight but featureful, and easy-to-use e-mail client (mailer, MUA).
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The addons extend Thunderbird's functionality making it by far the best email client ever made.