Endless OS takes a rather different approach to most Linux desktops, and that has a direct bearing on which email client makes sense. It is an immutable, consumer-friendly system built around OSTree, with applications primarily delivered as Flatpaks from Flathub rather than through traditional distro packages. That means the best choices are not simply the most popular mail programmes, but the ones that integrate cleanly with a Flatpak-first workflow, behave well on GNOME-based desktops, and do not depend on a lot of low-level system tinkering.

In practical terms, Endless OS is best suited to users who want a stable desktop for everyday work, schools, families, and non-technical home users. It usually ships with a GNOME-like experience, often with a simplified application model and minimal maintenance overhead. That also means classic package managers such as apt, dnf, or pacman are not the normal route on this platform. If an email client is available as a Flatpak, that is generally the cleanest option. If it only comes as a .deb or .rpm, it is usually not appropriate for Endless OS unless you are intentionally working outside the standard model.

For that reason, the shortlist below focuses on clients that are genuinely realistic for Endless OS, and I have included Proton Mail and Tuta Mail as requested because both are compatible through Flatpak. I have deliberately avoided options that rely on distro-native packages the system does not normally use.

The strongest recommendation for Endless OS, in my view, is to stay within the Flatpak ecosystem and choose a client that is comfortable in a GNOME environment. That immediately makes Geary and Evolution the two most sensible general-purpose candidates, with Thunderbird as the more powerful alternative for users who need broader compatibility or more advanced mail handling.

There is also a clear distinction between “mail client” and “mail service app” here. Traditional desktop clients like Thunderbird, Geary, and Evolution are ideal if you use IMAP/SMTP accounts from a variety of providers. By contrast, Proton Mail and Tuta Mail are best if you already use those services and want their dedicated desktop wrappers. On Endless OS, that distinction matters because the desktop is intentionally simple and stable you want software that installs cleanly and updates through the same Flatpak route as everything else.

Below is a more detailed breakdown of the five most relevant options.

Evolution

Evolution is probably the best “serious work” email client for Endless OS. It is available as a Flatpak, which makes installation painless, and it feels at home on a GNOME-based desktop. Beyond mail, it also handles calendars, contacts, tasks, and groupware-style workflows, so it is a particularly strong choice if you use Microsoft 365, Exchange, or a business IMAP account with calendar synchronisation.

Why it suits Endless OS:

• Flatpak availability fits the Endless OS application model.
• GNOME integration is very good, so it looks and behaves naturally.
• It is excellent for users who want mail plus calendar in one place.
• It is a mature application, which matters on a stable desktop where reliability is more important than novelty.

Potential downside: Evolution can feel a little heavyweight if all you want is a simple inbox. On modest hardware, Geary may be a better day-to-day fit.

Geary

Geary is the cleanest, simplest choice on Endless OS. If the user is not trying to manage multiple shared calendars, complex folder structures, or enterprise integrations, Geary gives a pleasant and uncluttered email experience. It is also a very good option for laptop users who want something that starts quickly and stays out of the way.

Why it suits Endless OS:

• It is available as a Flatpak via Flathub.
• The interface is minimal and approachable, which matches Endless OS’s user audience.
• It is less demanding than Thunderbird or Evolution.
• It is well suited to common IMAP providers and simple personal mail use.

Potential downside: Geary is not as feature-rich as Thunderbird or Evolution, so power users may outgrow it.

Thunderbird

Thunderbird remains the best all-round desktop mail client in terms of ecosystem, add-ons, and sheer familiarity. On Endless OS, it works well precisely because it is available as a Flatpak, alongside other packaging formats that are useful on more traditional Linux distributions. For Endless OS, though, the Flatpak is the route that matters.

Why it suits Endless OS:

• Flatpak support makes deployment straightforward.
• It handles almost any IMAP/SMTP setup with ease.
• It is ideal if you use multiple email accounts from different providers.
• It offers powerful filtering, search, and account management.

Potential downside: Thunderbird is more complex than Geary and a bit less streamlined than Evolution on a GNOME-centric system. If the user is a beginner, it can feel like more than they need.

Proton Mail

Proton Mail is a sensible choice only if the user already lives in the Proton ecosystem. On Endless OS it is usable because Proton provides a desktop app, including a Flatpak package path, which fits the distribution’s app strategy nicely. The advantage here is obvious: a native desktop wrapper for a privacy-focused mail service without needing to stay in the browser all day.

Why it suits Endless OS:

• Flatpak compatibility makes it a practical fit.
• Strong privacy features for users who prioritise encrypted communication.
• Good for people already paying for or relying on Proton services.

Potential downside: Proton Mail is not a universal mail client in the same way Thunderbird is. If your accounts are spread across several providers, a conventional desktop client may be better.

Tuta Mail

Tuta Mail is much the same story as Proton Mail from a deployment perspective: it is suitable on Endless OS because a Flatpak is available, so installation fits the distro’s intended workflow. The client is especially appealing for users who value privacy and want a dedicated desktop app rather than always using the web interface.

Why it suits Endless OS:

• Flatpak makes it straightforward to install and update.
• Privacy-first approach is attractive on a family-friendly, general-purpose OS.
• Very simple to use if you are already committed to Tuta.

Potential downside: like Proton Mail, it is best viewed as a service-specific client rather than a universal mail workhorse.

What I would actually choose on Endless OS

If you want the most practical recommendation, I would rank the choices like this:

1. Geary for simple personal email and the cleanest user experience.
2. Evolution for business users, calendar integration, and more demanding workflows.
3. Thunderbird for power users or anyone with multiple accounts and a need for flexibility.

If the user specifically uses privacy-focused hosted mail, then Proton Mail and Tuta Mail are both perfectly workable on Endless OS, but they should be chosen because of the service, not because they are the best general mail clients.

How to install and configure the best choices

1) Geary

Geary is usually the first client I would suggest on Endless OS when the requirement is “just make email work” without clutter.

Installation is normally through the software centre or the Flatpak frontend, depending on the Endless OS build. If you prefer the terminal and Flatpak is enabled, the command is typically:

flatpak install flathub org.gnome.Geary

Configuration steps:

1. Open Geary.
2. Choose Add Account.
3. Enter your name, email address, and password.
4. If your provider supports it, let Geary auto-detect IMAP and SMTP settings.
5. For providers with two-factor authentication, create an app password if required.

Best practice on Endless OS: keep the setup as standard IMAP unless your provider explicitly requires something else. Endless OS is happiest when the application layer remains simple and self-contained.

2) Evolution

Evolution is the better choice if the user needs calendars, contacts, or business email. On Endless OS, Flatpak remains the cleanest installation path.

flatpak install flathub org.gnome.Evolution

Configuration steps:

1. Launch Evolution and start the account assistant.
2. Select the mail provider or choose IMAP/SMTP manually.
3. Enter your details and authenticate.
4. If you use Microsoft 365 or Exchange, allow the account wizard to discover as much as possible automatically.
5. Enable calendar and contact sync if offered during setup.

One useful point on Endless OS: Evolution’s GNOME-friendly interface means it blends in better than many cross-platform clients, which matters for users who are not especially technical and want the desktop to feel coherent.

3) Thunderbird

Thunderbird is the strongest general-purpose option for mixed account environments. Again, Flatpak is the best fit for Endless OS.

flatpak install flathub org.mozilla.Thunderbird

Configuration steps:

1. Open Thunderbird and select Email when prompted to add an account.
2. Enter your name, address, and password.
3. Accept auto-discovered IMAP and SMTP settings where available.
4. For privacy-oriented providers such as Proton or Tuta, use the provider’s recommended settings or app-specific guidance.
5. Set up folder synchronisation and message filtering once the account is working.

On Endless OS, Thunderbird is the best choice if the machine is shared or if the user has several accounts from different services. It is also the most future-proof of the three because of its broad compatibility.

Why some other options are less suitable on Endless OS

Betterbird is a good Thunderbird derivative, but the packaging on offer is not ideal for Endless OS because it is distributed as a tar.xz archive rather than a Flatpak. That means more manual handling and less integration with the system’s usual app install model.

KMail / Kontact technically offers a Flatpak route, but this is a GNOME-led distribution and KDE PIM tends to feel more at home on Plasma desktops. It is not wrong, merely less natural.

Similarly, clients such as Mailspring, Claws Mail, Balsa, Sylpheed, aerc, NeoMutt, and Alpine are either distributed in ways that are less aligned with Endless OS or are aimed at more specialised users. The terminal-based clients in particular make sense for experienced administrators, but they are not the right first choice on a family-focused immutable desktop.

Recommended mail services for Endless OS users

If you are choosing a service to pair with one of the clients above, these are the ones I would recommend most often for Endless OS users:

• Proton Mail — Best if privacy is a priority and you want a polished, secure ecosystem with a desktop app that fits well on Endless OS.
• Tuta Mail — Another strong privacy-first option, especially if you prefer a simple model and a dedicated desktop client.
• Fastmail — Excellent for people who want reliable IMAP, solid calendars, and a very professional service without unnecessary fuss.
• Mailfence — A good fit for users who want privacy-minded email with standard protocols and decent interoperability.

My practical recommendation is straightforward: if you want the easiest, cleanest Endless OS experience, use Geary with a reliable IMAP service such as Fastmail. If you need more features, use Evolution. If you need broad compatibility and more advanced control, go with Thunderbird. And if you are already committed to encrypted ecosystems, Proton Mail or Tuta Mail are both sensible on Endless OS because their Flatpak support aligns well with the distro’s design.