Best Email Client for Linux : A Detailed Comparison

The email client, along with the word processor, is probably one of the most recognizable pieces of software on the desktop. They come in all shapes and sizes, from standalone lightweight command line clients, to massive personal information managers (PJMs), which do a lot more than just check email.

Email clients are especially important for the business user but are useful even for those not dependent on a corporate email server. Virtually all email clients can now hook up with online webmail services such as Gmail and Yahoo Mail. Even if you don't use them to check your email on a daily basis, they’re handy to keep an offline backup of all your email in case of problems with the service.

There are various factors you need to consider when selecting a client. What type of user you are and how you want to use it are the most critical. If you're an enterprise user fetching email from the corporate email server, you'll probably have the client running all the time, so it needs to be well• integrated into the desktop. If you're a home user, though, who only wants to back up email from an online service, your demands are very different.

How we tested

We ran all the email clients on a 2.1GHz dual-core laptop with 2GB of RAM. While they all work across distributions, for best results we ran them on their recommended platforms. That is, KMail atop KDE and Evolution under Gnome.

For a fair comparison, we used the latest offerings of each of the clients. KMail 4.7, released as part of KDE SC 4.7 was installed on OpenSUSE 11.4. The latest version of Evolution 3.0.2 requires libraries shipped with Gnome 3, and so we installed it on top of Fedora 15, which also hosts our Thunderbird and Claws Mail installation. Zimbra Desktop creates desktop icons, which have no place in Gnome 3, so we installed it on Ubuntu 11.04.

An email client should, at the very least, be able to handle thousands of emails without a drop in performance, compose messages offline, and be secure - just some of the features we're scoring on.

Desktop integration
Should you stick with your desktop's default?

Almost all the clients covered here are cross-platform and can run on any distribution. While it's good to have a choice, all distributions and desktops ship with a default email client, so Gnome has Evolution and KDE has KMail.

Traditionally, this also meant that Evolution was the default on Fedora and Ubuntu and KMail on OpenSUSE and Mandriva, among others. But the latest releases of these distributions, desktops and email clients have changed the situation somewhat.

Since Evolution now requires Gnome 3 libraries. Ubuntu will switch to Thunderbird as its default email client with the 11.10 release. KMail is one of the weakest clients in our selection, and we aren't the only ones who think so: in the latest Mandriva release it's also been replaced by Thunderbird.

Using the default client does have obvious advantages. For example, in Gnome, you can right click on a file in the Nautilus file manager; select Send To and specify email, to email the file as an attachment to a message. This launches a compose message window with the selected file listed as an attachment, so you don't have to explicitly launch Evolution in order to compose a message.

You can do the same with KMail on KDE in the Dolphin file manager by right-clicking a file and selecting Actions> Send To.

Default clients by definition, though, don't suit everyone. They have to cater for a large section of the user base, which is why KMail and Evolution aren't just email clients but PI Ms. which can create to-do lists and schedule reminders. This is too much functionality for someone who only wants a client to back up email.

Almost all of the clients support the MBOX mailbox file format. Claws Mail offers it via a plugin. The MBOX format stores messages concatenated into a simple text file. MAILDIR and MH are alternate formats.

The format in which mail is stored is important when you have to shuttle between clients. The format you export your mails in from one client, should be supported by the client you import mails into, or you will have to convert the mail into a supported format before importing it.

If you have to use multiple machines, running different operating systems, you might want to choose a popular format such as MBOX, which is supported by email clients on all distributions and operating systems.

While KMail and Evolution are only available for Linux distributions, Claws Mail, Thunderbird and Zimbra Desktop can be installed on any Windows, Mac or Linux machine.





Claws Mail


A photo-finish between Thunderbird and Evolution.

IMAP Support
How does it behave with webmail?

Most home users will want to hook up their email client with one of the popular webmail services. When configuring your account, you need the SMTP and I MAP settings, port numbers to connect to and whether or not to use SSL etc.

Of the five clients in our list, Evolution, Zimbra Desktop and Thunderbird can fetch settings from the IMAP server. This means you don't have to specify the port number or the SMTP settings to configure your account. KMail can determine what authentication options are supported, but only after you point it to the IMAP server. Claws Mail has to be manually fed all of the server settings.

Good email clients should help you configure the account with minimum effort, but that's only half the picture. How well the clients interact with the webmail service is also important.

You can compose messages offline with Zimbra, Evolution and Thunderbird, which will be sent automatically when you go online. Claws Mail however doesn't automatically send queued messages.

When importing messages, all clients connect to the webmail service to create a folder tree. You can then import messages into the folders. Claws Mail randomly sends old messages to the inbox, creating duplicates when you import from an MBOX file. Evolution is best at creating folders and importing messages. KMail provides the most import options, and imports messages without errors, but it doesn't display the message body. Messages downloaded from the internet are displayed without fault.





Claws Mail


Thunderbird needs to provide better importing support.

User experience
But they all look the same! Or, do they?

The purpose of an email client is rather simple: it fetches your emails, displays them in a neat interface, lets you easily compose and send messages and offers additional features such as search, labels etc.

The first email client, although nothing like what we have today, showed up almost a half century ago. Modern email clients, too, have existed for a few decades now and yet.

Despite the advancing years and changing email norms, most look almost exactly the same as their ancestors did. Comparing email client interfaces is almost like comparing keyboard layouts on different laptops. The layout is pretty much the same, and yet some are better than others. Email clients, which are very similar in terms of feature sets and usefulness, are no different. Some, however, steal the show by offering a little bit extra.


A very typical three-panel view, which is standard for most clients. Since it's a PIM, you get to choose between Mail, Calendar or Tasks using buttons on the bottom-left. You get the threaded message view by default. There's no visible difference between a threaded message and standalone messages, except for the +and -signs in the subject line to denote collapsed and expanded threads. Press Ctrl+ T to turn off threaded view. You can search for messages in the current folder, current account, or all configured accounts and create custom searches. It even lets you save searches, and create folders for them. Attachments aren't displayed inline by default. Depending on the type, however, you can choose to view them inline or with the default associated application.


Thunderbird is rather bare, especially compared with Evolution or Zimbra Desktop. This is primarily because various options are either clubbed together into one button, or not located on the Mail toolbar at the top. For example, the Delete, Forward and Reply buttons show up in the bottom panel when reading a message. Searching is one of the best features of Thunderbird and puts it miles ahead of the competition. Results show up in a new tab. with a year /month timeline and various additional filters to help you zero in on the message you want. The threaded view is not the default, but can be enabled if you click View > Sort By> Threaded. You can also archive messages, but archived messages can't be searched and you must specify an archives folder when setting up your email account.

Beam me up Scotty. Yes, now!

Mail boxes can grow to several GBs in size and so it's very important for email clients to handle a large number of messages with ease. Performing searches on thousands of messages may seem like a daunting job, but it's an everyday task for mail clients. We tested the search and general performance of the clients using a 450MB MBOX file.

Evolution took about 15 minutes to import the file. When searching, it provides near instantaneous results. Most clients let you compose messages while importing, but not Claws Mail, which is unusable. It took 30 minutes to import the same MBOX file.

We're confident Thunderbird is untouchable where Search is considered. It displays the results in a separate tab with many additional filters such as Starred, From Me, and List of Contacts.

KMail fares so poorly because very little actually works as advertised. For one, it doesn't display the message body when importing messages from a file. This mostly defeats the point in importing messages or migrating to KMail from any other client.

Of all the clients in our list, Zimbra Desktop was the slowest in performing regular tasks such as switching mail folders, but only marginally. While it can import messages, it needs them in TGZ format. This isn't a problem per se, but the additional step of converting exported messages into TGZ is a nuisance.

Claws Mail

Although not too shabby, the interface could use some work. The left panel appears crowded when it displays read, unread, and total number of messages in each folder. Change this setting under View > Set Displayed Columns> In Folder List. There are various built-In layouts to choose from. Click View> Layout and cycle through the five options to find one that suits you - the Wide Message and Three Columns layouts are ideal if you have a wide screen. There's no search bar in any of the layouts, and the toggle search button is so buried in the message list panel, it might as well be invisible. You can right -click a message to create filter and process rules. Process rules mean defining actions such as move, copy, delete, forward etc.


When you first launch KMail, it will terminate with a 'Failed to fetch the resource collection' error. KMail doesn't have a default incoming mail directory configured, which causes this error. The workaround involves using Akonadi to specify a maildir location for KMail. To do this, launch the Akonadi Configuration tool and point the Local Folders to -I .kde4/share/apps/kmail2/. The three-panel interface presents messages grouped by day/month/year, depending on the number of messages in the folder KMail does the threaded view better than the other tools, using line spacing to denote replies to messages in a thread. The search bar at the top can be used to search for messages, and you can use the drop-down list on its right to refine your search. For example, choose Has Attachment to limit your search to messages with attachments.

Zimbra Desktop

Although Zimbra Desktop also provides a three-panel interface, it does things differently enough to impress us. It does a lot more than just email but despite its many features, the interface is neat and clean. There are plenty of tabs at the top that let you move between Preferences, Mail, Calendar, Tasks and so on. The search bar produces near immediate results, searching in the subject, header, and message body. The Advanced button to the right of the search bar coughs up even more useful options to help you narrow down the results and lets you search Spam and Trash. Zimbra lets you save searches as well, a feature it shares with Evolution. Zimbra also supports threaded view, but it's even worse at identifying threads than Evolution. To mark a message as spam, select it and click Spam - no configuration required.





Claws Mail


Thunderbird and Evolution lead the pack here.

Besides email
PIMp my email.

The all-in-one nature of some of the clients in our collection deserves special mention. Not all users would want their email client to set up reminders and double up as a calendar, but if these are things that you use daily, it's probably best to use just the one tool, rather than several.

Still, you don't have to necessarily go with one of the advertised overachievers. Most other tools offer the same functionality as PIMs via extensions and plugins.

Evolution, Gnome's official PIM, provides a calendar, address book and task list, which is different from your calendar appointments. On KDE, KMail is part of Kontact, KDE's PIM software suite. The other applications that make up the collection are KaddressBook, Akregator and KOrganizer.

Thunderbird is primarily for email but there are plugins for everything else. The vanilla Thunderbird installation is not a PIM but the Mozilla Lightning extension will add the functionality. Its built-in RSS/Atom reader means it can also be used as a simple news aggregator. Additional features are available via other extensions.

Claws is similarly a news and mail email. It has an address book and plugins for a calendar, RSS aggregator and more. Apart from email, Zimbra does contact management and document handling, and has a calendar and task list. You can edit documents such as spreadsheets on the fly and include them in your emails.





Claws Mail


There's no catching up with Zimbra Desktop.

Is your client internet-proof?

Evolution lets you choose between SpamAssassin and Bogofilter as the spam filtering tool of choice. Of course, you need to make sure they're installed on your system before using them. If not. Evolution won't complain about missing packages, which is very odd. You'll also need to install the relevant Evolution plugin. Finally, you need to configure your junk mail settings. These are under Edit > Preferences > Mail Accounts > Edit > Receiving Options. You should also look at Edit > Preferences > Mail Preferences >Junk.

Thunderbird has a very advanced junk mail filter, which learns and improves its filtering depending on what you mark as spam. All incoming messages pass through the filter, and you can get Thunderbird to warn you about potential phishing emails, and also when a link in a message is leading you to a website other than the one indicated in the URL.

Claws Mail, if you compile it yourself, provides several useful plugins in the core package. But if you install it via your distribution's software repositories, you must install the plugins as well. Load them under Configuration > Plugins > Load. Next head to Configuration> Preferences > Plugins > SpamAssassin. Read the Claws Mail Plugins FAQ on the project's website, which covers the additional steps.

KMail fares better than Claws Mail in terms of security, at least at first glance. Click Anti-Spam to launch a wizard that will automatically detect if there's a tool, such as SpamAssassin, available and enable it.

You only need to mark messages as Spam or Ham to train SpamAssassin, but when you flag a message, a popup dialog appears telling you to wait while the message is transferred. Nothing happens and KMail is then unusable. An Anti-Virus wizard is also on offer, but good luck trying to get that to work - we didn't have that much joy with it.

You can encrypt messages when sending emails but only if you already have encryption keys on your system. None of the tools let you create keys from the interface itself, except for KMail, which can create keys when defining your identity.

With the other clients, you must use the distribution's key management program, whether it's Kgpgor Seahorse, to create keys which you can then use to encrypt messages.





Claws Mail


Only Zimbra and Thunderbird don't need spam plugins.

Add-ons and plugins
Accessories for your client.

As useful as the default feature set is, it's always good to know that additional features, even if you don't need them now, are available should the need ever arise. All clients release plugins officially, and these are a nice way to enhance functionality.

Thunderbird has the most extensive list. The add-ons page provides a categorized list of available extensions such as Contacts, Message Reading, Privacy and Security. You can also scroll through the Most Popular list on the left. Also available are dozens of themes that you can use to change the client's appearance.

Evolution's default installation already has several plugins installed and enabled. In fact, many of its basic email features, such as Mark All Messages as Read, are also a plugin.

Instead of Thunderbirds extensive add-ons database. KMail has Tools. Most aren't written by the KMail team, and some are too old to be of any use on recent releases.

Claws Mail is built on the premise that you will extend it with plugins as and when you need them. There are two categories - Standard is shipped with the package and will be installed if you manually compile Claws. Extra plugins can be downloaded from the website. If you install Claws via the software repositories of your distribution, you will have to separately install the plugins.

Zimbra Desktop's plugins are called Zimlets. The website offers a categorized list such as Contacts and Mail. Note that not all Zimlets work on all platforms.





Claws Mail


The Final Verdict

There are hordes of email clients out there but we limited ourselves to the ones that would be useful for the most users. This is also why clients that work on the most number of platforms score higher than those that don't Cross-platform clients provide a consistent interface across operating systems, and make it easier for you to import/export email when switching platforms.

Another important feature is the extensibility of the client and having a diverse range of plugins is useful when it comes to customization.

A couple of years ago, a lightweight client would have made sense but with hardware prices on a constant downward spiral, we wouldn't trade features for a minor bump up in performance.

We see no reason for recommending proprietary email clients either - in our experience they're dwarfed by their open source cousins.

After putting the clients through their paces, Mozilla’s Thunderbird came out on top. You can run it on any desktop environment and. of all the clients in this roundup; it officially supports the highest number of operating systems.
Mozilla moans

We aren't overly impressed with Mozilla's 'release often' strategy but we really can't find any faults with the client itself. It must be noted, though, that although Thunderbird 5 was pretty zippy on our dual-core laptop. Graham wasn't impressed by its performance on an Atom-based netbook in his review in LXF149.

If you're running a Gnome-based distribution, you could stick with Evolution, mostly because of its integration within the desktop. The newer version's need for Gnome 3's libraries means it's getting trickier to run it on Ubuntu, though.

Despite KMail's integration with KDE, we weren't impressed. Neither are some developers of KDE-based distributions, such as Mandriva, which has replaced it with Thunderbird in the latest version of its distribution.

Claws, the lightweight and zippy email client, is best paired with slim line desktops such as Xfce.

Also consider…

First up, there are many more email clients than the ones we've included here. We included tools that offered a complete email solution, which meant having to exclude our all time favorite, Mutt. It's a wonderful lightweight client, but as its text-based many users would just skip over it. Plus, it requires additional tools such as Procmail to filter messages.

We also had to pass up on popular browser-based clients such as RoundCube and SquirrelMail. These are shipped with popular web-hosting control panels such as cPanel, and look and feel like their desktop brethren, except for the fact that they run atop a web browser.

There are also those that leverage code from other clients, for example SpiceBird and Seamon key, which are both based on Thunderbird. Another popular option we've omitted is Opera Email, an extension to the Opera web browser. If you use Opera, you should definitely take this for a spin.

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