Top Alternatives to Opera Mail

Thunderbird is a free, open-source email client developed by the Mozilla Foundation, offering robust features for managing multiple email accounts, integrated chat, and RSS feeds. Known for its extensibility and focus on user privacy and security.

Microsoft Outlook is a comprehensive personal information manager designed for managing email, contacts, calendars, and tasks.

Apple Mail is the default email client for macOS, iOS, and watchOS, offering a seamless and integrated email experience across Apple devices with features like rich text editing, multiple account support, and robust organization tools.

eM Client is a comprehensive email client for Windows and macOS, integrating email, calendar, contacts, tasks, and chat into a single application. It offers robust features for managing multiple accounts, advanced security options, and a user-friendly interface, making it a powerful alternative to other popular email applications.

K-9 Mail is a free and open-source email client for Android, renowned for its focus on privacy, security, and extensive customization options. It supports multiple account types including IMAP, POP3, and Exchange.

Evolution is a comprehensive personal information manager for the GNOME desktop environment, designed to manage emails, contacts, calendars, and tasks. It provides a unified interface for various communication and organizational needs.

Mailspring is a modern, fast, and free desktop email client for Mac, Windows, and Linux. It offers a beautiful interface, powerful features like unified inbox, email tracking, and broad platform support for an enhanced email experience.

Claws Mail is a powerful yet lightweight, open-source email and news client built on GTK+. It's known for its speed, stability, rich feature set, and high degree of customization, making it an excellent choice for users demanding control and efficiency.

Geary is a modern email client designed for the GNOME desktop, emphasizing a conversational view for streamlined email management. It offers a clean interface, supports multiple accounts, and integrates with the GNOME environment to provide a cohesive user experience for organizing and sending emails.

The Bat! is a secure and powerful email client for Windows designed for users who prioritize privacy, speed, and efficient email management, especially for handling large mail volumes.

Sylpheed is a free and open-source email and news client known for its lightweight design and speed, focusing on usability and efficient handling of large email collections without burdening system resources.

OpenProject is a powerful, web-based open-source project management software designed for teams of all sizes. It offers comprehensive tools for managing projects, tasks, teams, and communication in one centralized platform. Ideal for organizations prioritizing collaboration, flexibility, and data control.

Spark is a powerful and intelligent email client designed to enhance your productivity and streamline your inbox management. It offers a range of features like smart inbox organization, email scheduling, and integrations with popular services, making it a comprehensive solution for busy professionals and individuals alike.

Polymail is an advanced email client for macOS and iOS, built to enhance productivity for professionals using Gmail. It goes beyond basic email functions with robust features like email tracking, scheduling, and team collaboration tools, all wrapped in a sleek and intuitive interface.

<p>MailMate is a powerful, keyboard-centric IMAP email client for macOS designed for users who demand advanced email management capabilities and a highly customizable workflow, featuring strong Markdown integration and robust search features.</p>

Microsoft Mail and Calendar is the default email and calendar client included with Windows, providing integrated tools to manage your communications and schedule.

Foxmail is a robust and user-friendly freeware email client for Windows. It offers comprehensive support for popular email protocols like POP3, IMAP, and Exchange (ActiveSync), providing a centralized platform for managing multiple email accounts. Key features include a portable option, calendar integration, and time-saving mouse gestures.

TypeApp is a sophisticated mobile email client designed for managing multiple email accounts effortlessly. It provides a unified inbox, push notifications, calendar integration, and a range of features to enhance email productivity on the go.