SME Server, formerly known as e-smith, sits in a rather different corner of the Linux world compared with the usual desktop-first distributions. It is primarily a server platform, built around straightforward administration, web-based configuration, and a conservative, appliance-like approach. In practical terms, that means email clients are usually not installed on the server itself for day-to-day reading of mail, but rather on a connected workstation or admin desktop used to manage mailboxes, inspect logs, or troubleshoot accounts. That distinction matters quite a bit when choosing an email manager: the best option is not simply the one with the most features, but the one that matches the packages available, the desktop environment in use, and the way SME Server administrators actually work.

On SME Server, package management is not the same as on a mainstream Ubuntu or Fedora desktop. Historically, the platform is closely tied to RPM-based systems, which makes RPM packages the most natural fit. If you are building out a management workstation around SME Server, you are typically looking at a desktop environment such as GNOME, KDE Plasma, or something lighter like XFCE or MATE installed on a separate client machine. In that setting, compatibility, low maintenance, and good IMAP/SMTP handling matter more than glossy extras. Also worth noting: SME Server itself is often used with mail services such as mailboxes, aliases, and server-side filtering, so a client that behaves well with IMAP, multiple identities, and encrypted authentication is particularly useful.

For this reason, the shortlist below focuses on three to five clients that are genuinely sensible for an SME Server-centric environment, while always including Proton Mail and Tuta Mail where their packages are compatible. I have deliberately avoided treating this like a generic Linux desktop comparison. Instead, this is aimed at the realities of an SME Server deployment: RPM compatibility, server administration workflows, and practical support for common desktop environments used alongside the server.

Here is the comparison table.

From an SME Server perspective, the shortlist above naturally prioritises Thunderbird and KMail/Kontact, with Mailspring as a practical third choice and Proton Mail or Tuta Mail included where relevant to your account type and packaging constraints. If the workstation is RPM-based, those three desktop clients are especially convenient. Thunderbird remains the safest overall recommendation KMail makes sense for KDE users Mailspring is the more modern but less server-centric option and Proton/Tuta are worth considering if your actual mail workflow lives inside those ecosystems.

Below is a more detailed breakdown of each of the selected clients, with specific attention to SME Server usage rather than generic desktop marketing.

1. Thunderbird

Thunderbird is the most sensible default choice for a workstation that talks to SME Server. It is available in RPM form, which fits naturally if your management desktop is running an RPM-based distribution or a workstation built in the same ecosystem as the server. It also handles IMAP exceptionally well, and that matters because SME Server deployments often rely on IMAP rather than local mailbox storage. Thunderbird is also comfortable with multiple accounts, manual server settings, and authentication methods that are common in real business environments.

Another practical advantage is flexibility. If you are connecting to SME Server mailboxes, aliases, or multiple domains, Thunderbird copes cleanly with identities and folders. Add-ons are useful too, although in modern setups I would recommend keeping extensions minimal unless there is a clear operational need. For admins, the main appeal is that Thunderbird does not fight you when dealing with standard mail protocols, and it is available in a straightforward package format for RPM systems.

2. KMail / Kontact

KMail / Kontact is the strongest option for a KDE Plasma workstation. If your SME Server administration desktop uses KDE, this is a genuinely polished choice. The RPM package is available, which makes it suitable for the same ecosystem that SME Server itself is naturally closest to. Kontact is more than just email: it brings calendar, contacts, and scheduling together, which can be useful where mail administration overlaps with office coordination.

That said, KMail is best chosen deliberately rather than casually. It is powerful, but it is also more opinionated than Thunderbird and tends to suit users already comfortable within the KDE stack. If your desktop is GNOME or XFCE, KMail is less attractive. If you are on Plasma and want a well-integrated PIM suite for handling mail alongside calendars and tasks, it is hard to dismiss.

3. Mailspring

Mailspring is a decent modern client for an admin workstation, especially if you want a cleaner interface and are not tied to a specific desktop environment. It is available as RPM, which helps in SME Server-adjacent environments. Mailspring feels more contemporary than some older desktop mail clients, and for users who spend a lot of time triaging mail rather than managing deeply nested server structures, it can be pleasant to use.

The caveat is that Mailspring is not my first choice for the sort of hands-on mail administration often associated with SME Server. It is usable, certainly, but it is not as naturally aligned with server-side IMAP workflows as Thunderbird, and it is not as deeply integrated into a Linux PIM environment as Kontact. Still, for an administrator who wants a tidy, accessible client on a desktop workstation, it deserves consideration.

4. Proton Mail

Proton Mail is included because its RPM package makes it compatible with the sort of desktops commonly used around SME Server. It is important to be precise here: Proton Mail Desktop is primarily for managing Proton accounts. It is not the best tool for directly managing classic SME Server mailboxes unless your organisation is actually using Proton for user-facing email and SME Server only for infrastructure or relay-related tasks.

Where Proton makes sense is in a mixed environment: perhaps administrators keep their secure operational mail on Proton while server-side domain mail remains on SME Server. If your mail workflow emphasises privacy and you already have Proton accounts, the RPM package means it can fit neatly into the same workstation estate. It is just not the best general-purpose client for native SME Server mailbox administration.

5. Tuta Mail

Tuta Mail is a similar story. It is compatible through AppImage and Flatpak, which makes it easy to run on many Linux desktops, but from the SME Server perspective it is still more of a service-specific desktop app than a general-purpose mail manager. It is a sensible choice if your organisation uses Tuta accounts, particularly where privacy-focused communications are a priority.

In an SME Server environment, Tuta is best viewed as a companion client rather than the primary way to manage the server’s own mailboxes. Still, because the package formats are available and easy to deploy on common desktops, it is worth including in the decision process for privacy-conscious users.

Which are most suitable for SME Server?

For this specific distribution and its typical use case, the ranking is fairly clear:

1. Thunderbird — best overall for SME Server-related mail work, especially on RPM-based desktops.
2. KMail / Kontact — ideal if the workstation is KDE Plasma-based and you want a richer PIM suite.
3. Mailspring — a comfortable modern alternative for admins who prefer a cleaner UI.
4. Proton Mail — only if you actually use Proton accounts and want RPM compatibility.
5. Tuta Mail — only if your mail lives in Tuta and you want AppImage/Flatpak convenience.

The main technical reason Thunderbird comes out on top is that SME Server is not a flashy desktop distribution it is a robust server platform that benefits from predictable, protocol-friendly clients. Thunderbird is excellent at plain IMAP, SMTP submission, multiple identities, and manual server entry. Those are exactly the things you need when dealing with a server-managed mail environment. KMail is great if you are in the KDE world, and Mailspring is pleasant, but Thunderbird is the safest recommendation by a clear margin.

How to install and configure the best choices

Thunderbird

On an RPM-based workstation, Thunderbird is usually the simplest and most dependable install. If you are using a modern Fedora-like or RHEL-like desktop, you can install it through the package manager or software centre. On SME Server itself, I would generally avoid installing a desktop mail client directly unless you truly need one locally it is better to run the client on an admin workstation.

Typical RPM-style installation example:

sudo dnf install thunderbird

After installation, launch Thunderbird and add your SME Server mailbox manually. Use the server’s IMAP hostname, usually the mail host that serves your domain. In a typical SME Server setup, that will be your domain’s mail server or the server’s own FQDN if it is handling mail directly.

Recommended configuration approach:

• Set incoming mail to IMAP rather than POP3.
• Use SSL/TLS for IMAP, typically port 993.
• Use SMTP submission with authentication, usually port 587.
• Enter the full email address as the username.
• Enable folder synchronisation if you need offline access.

Example settings you would normally verify:

IMAP server: mail.example.co.uk
Port: 993
Security: SSL/TLS
SMTP server: mail.example.co.uk
Port: 587
Security: STARTTLS
Authentication: Normal password
Username: user@example.co.uk

For SME Server administrators, Thunderbird is especially useful when checking whether a mailbox is behaving correctly, whether folders are appearing as expected, or whether a user’s SMTP authentication is failing due to credentials rather than server policy.

KMail / Kontact

If the workstation is KDE Plasma-based, KMail is a fine option. Installation on an RPM-based desktop is straightforward.

sudo dnf install kmail

When setting it up, use the same IMAP/SMTP principles as with Thunderbird. The main difference is that Kontact tends to encourage a fuller PIM setup, so you may also want to add calendar and contacts if your workflow justifies it. If the SME Server environment is being used by a small office that wants mail and scheduling in one place, this can be quite practical.

Best practice for SME Server use:

• Use IMAP for mailbox synchronisation.
• Keep sent and drafts on the server unless you have a reason not to.
• Verify the mail identity separately if you manage multiple domains.
• Prefer a dedicated KDE desktop, because the integration is better there.

Mailspring

Mailspring can be useful if you want a polished interface without digging too deeply into configuration complexity. On an RPM workstation, installation is normally just as easy.

sudo dnf install mailspring

During setup, choose manual configuration if the automatic account discovery does not immediately recognise your SME Server mail host. As with the other clients, use IMAP and SMTP with encryption. For administrators who monitor several mailboxes, Mailspring’s interface can be an advantage, though it is less “old-school mail admin” and more “business mailbox manager”.

Good use cases on SME Server-related desktops:

• Lightweight administration of a handful of accounts.
• Users who prefer a clean, modern UI.
• Workstations where Thunderbird feels too traditional and KMail feels too integrated into KDE.

Why I would not prioritise the others here

Several of the remaining clients are perfectly respectable, but they are a weaker fit for this particular environment. Geary, Evolution, Claws Mail, Sylpheed, and the terminal-based clients such as aerc, NeoMutt, and Alpine all have their merits. However, for SME Server they are either less common on the desktop estates usually used alongside the server, less convenient in RPM-based deployments, or simply less balanced for the kind of mailbox administration most people actually need.

That is not to say they are poor software. It is just that SME Server is not trying to be a cutting-edge desktop Linux system. Its strengths are stability, mail and service management, and predictable operation. The mail client should therefore be equally predictable and easy to support. Thunderbird fits that brief exceptionally well, KMail fits it well within KDE, and Mailspring is an acceptable modern alternative.

Recommended email services for this setup

If you are pairing a client with SME Server and also considering hosted email services, a few options stand out for their compatibility and reliability.

• Proton Mail — Strong privacy focus and a good fit if your organisation values encrypted hosted mail. It pairs naturally with the Proton Mail Desktop client.
• Tuta Mail — Another privacy-first service, particularly appealing if you want a lightweight, secure hosted mailbox alongside Linux desktops.
• Fastmail — Very solid for business use, with good IMAP support and a reputation for being straightforward and reliable with desktop clients like Thunderbird.
• Mailfence — Suitable if you want privacy features and standard protocol support without getting too far from traditional email workflows.

My practical recommendation would be this: use Thunderbird for the main SME Server-connected workstation, consider KMail / Kontact only if you are already committed to KDE Plasma, and keep Mailspring as a usable alternative for users who prefer a more modern interface. If your organisation’s actual mail service is hosted externally, Proton Mail, Tuta Mail, Fastmail, and Mailfence are all sensible choices depending on how much you value privacy, simplicity, and standard IMAP compatibility.

In short, SME Server rewards sensible, low-fuss tooling. For most administrators, Thunderbird is the best all-round answer, KMail is the KDE-native specialist, and Mailspring offers a polished modern alternative. The rest are either more niche or more service-specific, which makes them less compelling for a server-centred Linux environment like SME Server.