My use of Thunderbird is pretty much simple: email reception and sending, filter to find an email per date or sender, automatic filters to get emails directed to their folders or subfolders and use of address folders. Thunderbird is my default email client so I use it everyday. Thunderbird is super stable. I have been using the different versions over the years (more than a decade) and I never had a crash. One can easily create folders and subfolders. It's very convenient when you run a company with several projects and different emails per project. The active filters are a wonder. You can direct messages in the right folders and subfolders depending on the source, the subject, etc. The address folders are super handy when you need to run emails campaigns. I didn't have to use customer support so I don't really have an opinion on that

It provides notable privacy features, is fast, and highly customizable making it secure and personal to browser.

I have used Thunderbird for years across Windows, macOS, and Linux, and I’m a genuine fan of how it has evolved into a mature, privacy-first email and personal information management suite with a clear product vision anchored in open standards and extensibility. ✅ The unified Inbox model and multi-account architecture are implemented cleanly, with the option to keep account silos or work from a consolidated view when moving fast. Search, quick filters, message tags, and virtual/saved searches form a cohesive triad for handling large, multi-year archives and high-volume mailboxes without performance gimmicks. ✅ The desktop app covers the core PIM surface natively: email, calendar with recurring events and invites, contacts, and tasks, so switching contexts between messages and schedules happens in one place. It is not just a bolt-on calendar either; multiple calendars with color coding, standards-based invitations, and an address book that feeds autocompletion are available out of the box. The design accommodates different layout densities and panels, with classic, wide, and vertical views plus a competent three-pane default for triaging. ✅ On the mail layer, protocols and auth are first-class: IMAP and POP3 are supported with OAuth for providers that require it, TLS/SSL everywhere, and LDAP autocompletion for directories. Security posture is practical and thorough: built-in S/MIME, native OpenPGP on modern versions, phishing protection, remote-content blocking by default, and Bayesian junk filtering that learns as messages are trained. The privacy model is straightforward: no ad monetization, no data sales, and an open-source codebase stewarded by the Mozilla ecosystem with user donations instead of surveillance economics. ✅ Customization is a major differentiator. Themes, tags, per-folder behaviors, and an extensive add-on ecosystem let me tune workflows precisely, from message templates and “send later” behaviors to power tools like QuickFolders and Smart Templates without resorting to proprietary lock-in. The Configuration Editor provides deep control when advanced toggles are needed, while the standard settings surface remains sensible for daily use. Offline capability is native, so composing, searching previously synced mail, and organizing continues uninterrupted during travel or flaky connectivity, with sync catching up later. ✅ Thunderbird’s unified Inbox is designed for real multi-account operations instead of a cosmetic listing; color-coded account indicators and per-account folder trees make it easy to pivot between a global triage view and account-specific maintenance in a single session. Saved searches and message grouping add another layer of persistent, query-driven organization, which is invaluable for project mail, newsletters, or long-running vendor threads. ✅ Recent momentum on mobile completes the story. Thunderbird for Android is now a stable, privacy-focused companion that carries the project’s ethos to phones, built from the K-9 lineage and released officially with ongoing updates via Play Store and F-Droid. The team publicized the release cadence, import paths from K-9 and desktop, and platform availability, and the early reception suggests a healthy feedback loop and contributor inflow. For anyone who spent years wishing the desktop experience existed on Android with open-source principles intact, that milestone matters. ✅ The roadmap and communications are refreshingly candid. The project shares progress reports and long-term strategy in public, including an announcement of optional, paid “Thunderbird Pro” services designed as open-source, privacy-centric complements rather than a shift of the core client into paywall territory. The positioning is explicit: core Thunderbird stays free; optional cloud services like email hosting, scheduling links, large secure file transfer, and opt-in assistive features come later to cover server-side use cases while remaining standards-based and portable. It is rare to see an ecosystem that keeps both self-hosting and vendor-neutrality front and center while acknowledging modern collaboration needs. ✅ Onboarding is smoother than it used to be. Autodiscovery during account setup generally finds the right IMAP/SMTP parameters and ports, offers a manual override when needed, and supports OAuth flows cleanly for Gmail and Outlook without hidden caveats. Documentation covers both quick-start and deeper topics, and the community forum plus official support content are active and helpful, especially around unified folders and POP vs IMAP nuances. ✅ Daily ergonomics are strong. Quick Filter, tag hotkeys, compact headers, per-folder retention rules, and the ability to right-size notification behaviors contribute to a predictable triage rhythm. Message list performance on large mailboxes remains stable, and search indexing is fast enough to feel immediate on modern hardware. The calendar’s recurring event handling is robust, and invite parsing is consistent with major providers. The address book integrates with autocompletion and supports multiple sources without fuss. ✅ I also appreciate the project’s cross-platform discipline. Consistent support for Windows, macOS, and Linux means work environments are flexible, and configuration portability is practical when moving between machines or imaging new devices. For organizations and tinkerers alike, the combination of open formats, transparent configuration, and no lock-in is compelling. ✅ Finally, the Android app closes critical gaps on the go. It brings multi-account support with optional unified Inbox, respects privacy by default, supports OpenPGP via OpenKeychain, and lets me tune sync strategies for battery or immediacy. Distribution via Play, F-Droid, and direct APKs honors different trust and update models common in the open-source community. ✅ In short, this is a coherent, standards-first email and PIM platform that plays well with any provider, embraces transparency, and gives me deep control over workflow without trading privacy for convenience.