Linux Mail Clients Deep Dive- The Lightweight Options

E-mail has been around forever, predating even the web. Despite its age, and the continuous influx of new messaging platforms, it remains the most widely employed form of electronic communication. It offers a combination of reliability, ease of use, flexibility, with an open and non-proprietary structure that appeals to both new and seasoned users. When it comes to accessing e-mail the options are numerous and the choice can be deeply personal.

Most e-mail services offer web-based interfaces that can be accessed through any device and with any operating system. While this can provide users with basic functionality, many users require a dedicated mail client for expanded functionality, the ability to review messages offline, and for managing multiple accounts. In this series of reviews, the ItsMOSS team will review the various mail clients available to Linux users and share our experiences.

Geary, Claws, and KMail

My previous entry in this series (on Evolution) was focused on finding a full-featured mail client and personal information manager. With 8 different accounts that I monitor regularly including a mix of exchange and imap, and with multiple active calendars, the options are limited on Linux (or Windows or Mac for that matter).

However, not everyone has such a complex use case. For many people, the mail client is used with one or two accounts, and additional functions like calendar and tasks lists are unnecessary. In fact, even I don’t bother with my work accounts on my secondary systems. In this case, an enterprise-friendly client is not needed and one might consider lightweight options for a simpler interface.

I tried out Geary, Claws, and KMail, three lightweight mail clients that are in active development and suitable for those who don’t need a comprehensive information manager.


Claws is a free and open source lightweight mail client that is available in the repositories of most Linux distributions as well as Windows, MacOS, and BSD. It just celebrated its 20th anniversary. It initially started as a developmental branch of Sylpheed (Sylpheed-Claws) but was eventually forked and now appears to be more active then its parent development (Sylpheed’s latest release was January 2018).

Initial setup of Claws is fairly straightforward. You enter the basic details for the account (Full Name, Mail Address) and choose your server protocol. For many accounts you can then click autoconfigure and it will automatically pull the server details which is extremely convenient. Occasionally I have found that you will need to manually enter these details. Be forewarned that Claws will only work with IMAP and POP servers so you will need to look elsewhere if your email is hosted on an exchange server.

Once you have configured your account(s) the interface is fairly standard with an account list and folders on the left and message list with previews to the right. The default layout (message list above the preview) can be changed to three columns (account list, message list, and preview all alongside one another), wide message (the preview column runs the width of the screen under the account list and message list, wide message list (the message list runs the width of the screen over top of the account list and preview, or small screen (account list, message list, and preview are viewed one at a time and take up the whole screen). Personally, I found the three column to be the most visually appealing and functional.

Overall I found the user experience fairly decent in Claws. It isn’t the most visually appealing client, but the interface is simple to navigate and very fast. The toolbar is not overly complicated but that actually conceals a fairly feature rich environment (for a lightweight client). You have an address book, mail filtering system, and signature functionality (simply create a signature file in a text editor and then link it through account preferences, compose). This constitutes the key features in Claws, however this can be expanded slightly through plug-ins (available on the Claws Web site). For example, the ability to view .pdf or to receive attachment warnings.

The verdict:

This is a perfectly functional and fast client that does what it says. While it is not a solution for exchange accounts, for POP/IMAP accounts it gets the job done with no fuss. A worthy option.


Geary has been around since 2012, initially developed by the Yorba Foundation. According to Wikipedia, the original purpose of Geary was “to bring back users from online webmails to a faster and easier to use desktop application”. That is a mission that I can get behind!

Eventually Yorba stopped operations and, after a fork to Pantheon mail initiated by ElementaryOS, Geary became a GNOME project. It remains in active development, with the most recent stable release coming in September 2020.

Like Claws, Geary does not try to be a one-size-fits-all personal information manager, but remains a clean and simple email-only client. Geary is available in all major repositories and a flatpak is available.

On first boot you are met with a very simple welcome screen that asks you to choose your mail service (Gmail, Yahoo Mail,, other). If your account is with Gmail, Yahoo, or Outlook/Hotmail, Geary will automatically incorporate the server details. All that is needed is a login and password. For other IMAP/SMTP accounts you will require the server address and possibly ports to configure. It’s a bit more work than some clients (Claws, for instance, pulled the server details for most of my accounts) but still fairly straightforward. Like Claws, Geary does not work with exchange e-mail servers.

Once your client is installed, you are welcomed with a fairly modern and clean interface which is amongst the most visually appealing of all Linux mail clients.

Like Claws, it also has a very clean interface with limited buttons on the toolbar. However, behind the scenes it is also quite lean. The only option for changing settings is by clicking the little mail icon in the top left corner. This brings up options to edit accounts, a handful of preferences (automatically select next message, the look of the conversation pane, and sound options) and various help screens.

That’s it! No calendar, no task list, no address book, no filtering options or integration of other apps. It took me a while to find the option but it is possible to create signatures. Once your account is created go to the account list (from the mail icon in the top left) and choose to edit your account. At the bottom of the tab you can create a basic signature.

The verdict

Geary is never going to be mistaken for Thunderbird or Evolution in terms of the features it offers. But that’s the point. This is a lightweight mail client in the truest sense and it is very effective in achieving this goal. It shouldn’t be an option as a personal information manager but for basic e-mail usage it offers the simplest and most visually appealing interface of the lightweight mail clients that I have tried.


KMail is the e-mail component in Kontact, the personal information manager for the KDE desktop environment. It is designed to be used as an integrated PIM package, but individual components can be downloaded, including Kmail. KMail itself is available in the repositories of most Linux distributions.

I will start by saying that it is a bit of a misnomer to call KMail a lightweight mail client, particularly when used alongside the full Kontact suite. It is significantly heavier and more feature rich than Claws or Geary, but the lack of exchange integration and an incomplete integration of calendar and task features led me to include it alongside Claws and Geary.

Account setup starts off fairly simple. It is just a matter of entering your name, email address and password. KMail can find your provider settings from the internet by checking a box – this is quite effective and worked for every IMAP/SMTP account I tested. You can also enter the information manually if it does not work for some reason. Once this process is complete, KMail offers to configure email encryption with GNU privacy guard. This is somewhat unique amongst the mail clients I have tested. Certainly other clients are able to do encryption in this way (Evolution and Thunderbird have the option in the account settings and Claws has a GPG plugin), but it is rare to incorporate this into the setup process. For new users this might be a greater level of complexity than they are comfortable with, but advanced users may appreciate this.

Once you have configured an account, the interface is quite clean and simple with the typical account/folder list on the right and the message list and preview tab to the right. There is a simple list of actions in the top panel. This is fairly typical but I do find the interface to be slightly more modern looking and visually appealing than other clients (ie. Claws, Thunderbird, Evolution and even Geary).

KMail offers a handful of features like mail filtering, a very nice signature setup, and a rich plugin environment. Being a KDE entity it is also highly configurable with the ability customize toolbars, and virtually everything else. A pet peeve of mine was that sometimes when I would change a setting or appearance (i.e. width of columns) that the change wouldn’t be retained the next time I launched Kmail. I’m not sure if this was unique to me as I only tested in one system.

The verdict

Ultimately I find KMail as a standalone client to not really fit a use case for me. It isn’t really lightweight (Geary and Claws are far lighter) but it isn’t really a full featured personal information manager either. That’s where Kontact comes in. Kontact actually does a very nice job of incorporating separate applications for Mail, Addresses, Calendar, and Tasks together (it also incorporates a news reader and pop-up notes) such that it really does seem to be a single application that approximates the functionality of Outlook, Evolution, or Thunderbird. It has a more modern look than other Linux productivity managers with lots of customization options and a smooth interface.

So if I am thinking about at Kmail then it is within the Kontact suite and the peer group would be Thunderbird, Evolution etc… The big barrier for my own adaptation is exchange integration and unfortunately that is absent at the moment. (*I will be exploring this in greater depth and if I find a solution I will update this article accordingly). So Kontact is one to keep an eye on as a full featured client but for now, as a lightweight option or a comprehensive personal information manager it comes up short in my mind.

Final thoughts

When I am looking for a lightweight mail client, my personal choice is Geary. It is the best-looking, with a simple and highly functional interface. It is currently the client that I’m using for my children’s systems. Both Claws and KMail are functional options that have plenty to offer, but for a lightweight mail client I’m looking for the lightest and simplest with the cleanest interface — and that’s Geary.

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