Claws Mail vs. Thunderbird – A comparison

If you have been reading this blog for a while you know I have recently switched over from Thunderbird to Claws Mail. After all the fuss at Mozilla concerning Thunderbird I thought I would look for a replacement, not for immediate use, but for the future in case Thunderbird was shot down from it’s email flight.
Now that I have been using Claws Mail for a while I thought I would write up a comparison between Claws Mail and Thunderbird and maybe this way I can help some people making a decision.

I have been a Thunderbird user for years. I started using Thunderbird back in the days when I was still running Windows and I was looking for something to replace my Outlook Express. I chose Thunderbird because I also switched to Firefox and I was very happy with Firefox so gave Thunderbird a go. Over the years Thunderbird got better and better, more plugins came out and the functionality was outstanding.

I ran three plug-ins for Thunderbird:

  • Enigmail – Very very good PGP manager.
  • Signature Switch – To change my signature in my emails.
  • Folder something, I forgot. I’ll talk about it further down in the article.

I was really happy with Thunderbird especially when I made the move to Linux on my laptop, no need to use a different email client, just download and install Thunderbird and it was like things never changed. So why did you change you ask? Well like I said in the beginning of the post, all the fuss at Mozilla was my main concern.
When I started using Claws Mail it took some getting used to, not long though, because most the basic functionality is the same, compose an email, reply, create filters etc.

I’ll list some functionalities and how they compare between Thunderbird and Claws Mail

Filter creation

When I started creating filters I quickly fell in love with the automatic filter creation, it basically checks the email headers and when it detects mail listing headers it will tell you it’s using that, with Thunderbird I had to check the message source and determine which header to use.
Just like Thunderbird you can still create a filter manually and use any header you like, the only thing is that in Claws Mail that header isn’t remembered, so next time you create a filter by hand you’ll have to type the header again instead of selecting it from a pull down list.


The possibility for archiving in Thunderbird is limited to the mail account, at least by default, there might be a plug-in available, so for an account you can say you want to keep 30 days of mail for example. With Claws Mail you can create processing rules for every folder you create, and I for one have a rule for archiving the items in that folder and besides deleting mail unconditionally you can add conditions in the rule, like don’t delete mail you have tagged as Important.

It’s a longer process to set up archiving but I believe it’s definitely a very big plus for Claws Mail.


Thunderbird doesn’t support GPG natively and in all honesty that’s a good thing because it paved the way for Enigmail, THE GPG plug-in for Thunderbird. Claws Mail also doesn’t support GPG natively but they ship a plug-in with the default installation and you only have to load through the plug-in menu.

The big thing for about Enigmail is the fact you can set up rules for the use of signing and/or encrypting. So if you always have to encrypt your emails to a certain person, just set it up and forget about it, when ever you email the mail won’t be encrypted unless you mail that person. It was something I used a lot and it was the main reason why I switched back in the beginning from Claws Mail to Thunderbird. I decided to change the way I use GPG, like I will always sign my emails regardless who I send it to, that way I don’t have to use rules. I still hope Claws Mail will some day implement this feature though.

Folder management

This is way better in Claws Mail as it is in Thunderbird. In Claws Mail you have several options for your folders, I already mentioned processing rules, which are almost like filtering rules but not exactly. The other thing you can do is set which account to use and/or the recipient when you compose an email in that folder. This is especially easy for mail listing. In Thunderbird I used a plug-in for the last option.
There are several other options you can set per folder, I don’t use them but I can see them being useful, like a different dictionary for spelling.

Mail Listing

Claws Mail has default support for mail listings. Every mail listing has headers that tells you how to post, reply, subscribe, unsubscribe etc. These options are shown in the toolbar menu. For Thunderbird there’s a plug-in available that can do the same thing.


Unlike Thunderbird, Claws Mail doesn’t have native support for spam. They do have two plug-ins avalaible, one is a bogon filter, the other is a plugin that talks to Spamassassin. Personally I use Spamassissin which means you will have to install it on your machine, also Spamassissin is not the quickest software around but I can live with it.

Reading Email

Claws Mail’s default way to present the email is plain text. You need a plug-in to be able to read HTML formatted emails. The plug-in comes default with the installation, you just need to activate it. Like Thunderbird when you read a HTML email, images won’t load automatically but you can tell it to load them.
Another feature in Claws Mail is a button that will jump you to the next unread email, no matter if it’s in a different folder or a different mail box.


I don’t have numbers but Claws Mail response faster than Thunderbird. Besides the spam filtering using Spamassissin, Claws Mail is super fast.

Memory usage

Claws Mail uses less memory than Thunderbird. The use of plug-ins doesn’t have a big effect on the memory use in Claws Mail, I’m not sure what the impact of it is in Thunderbird.


In this area it’s Thunderbird that rules. There are hundreds of plug-ins available for #TB, unlike for #CM which only has a few. Personally I don’t need that many plug-ins and for the things I wanted to do in Claws Mail , and it wasn’t supported natively, there is a plug-in available. If you’re thinking about switching from Thunderbird to Claws Mail, you’ll have to check the reason why you use a plug-in in Thunderbird is supported natively in Claws Mail. If not, check if there is a plug-in available for #CM and if that’s not the case if you can live without the plug-in. I made the choice I could live without Enigmail and so far I haven’t missed it.

Well that’s about it, I hope it has been helpful. I’m not stating Claws Mail is better nor that Thunderbird is better. It all depends on what kind of user you are and you already know what my choice is.

This article is filed under the category Desktop and has the following tags associated with it: , , .
  • Nice comparison. As you said CM is super-fast and i like it. However availability of “Extensions” for almost anything is a big plus for thunderbird.

  • The reason Claws Mail is so fast is that it doesn’t really do much. I could write a tic-tac-toe program right now that will run faster than the one included in Gnome. That would be because it would be text-only, have a horrible interface, and lack most of the features people have come to expect. Much like Claws Mail actually.

  • David, where are you from ? what are you talking about ? you are not serious – are you ?

  • Lang

    The spam issue was a breaker for me. I use IMAP exclusively and couldn’t find a way to easily replace the junk mail controls of Thunderbird. I like to try different programs, but seeing that even after blocking most spam at the server, about 1/2 of the mail that actually makes it through is spam and by this point Thunderbird catches about 90% of that.

    I wish the junk mail controls were a little better. I’m all for the one tool for one job unix philosophy, but in this case I make the exception.

    Nice write-up by the way.

  • David Russell says:
    The reason Claws Mail is so fast is that it doesn’t really do much.

    Excuse me David, but you talk shit!
    I guess that you haven’t tried Claws Mail.

    Peter, a few enhancements to your comments…

    You talk about ‘native support’ for GPG and anti-spam. Since the Claws Mail team maintains and ships these plugins the line between native support and non-native support is quite blurred, imo. The main difference is that you have to initially load a plugin. 8 plugins are packaged with and built at the same time
    as Claws Mail, dependencies allowing, with 16 other plugins being packaged separately as ‘Extra Plugins’.

    Archiving: You can also Lock messages. In addition to folder-specific Processing, you can set Pre-Processing rules, which are global and are run before Folder Processing rules.

    Mail Listing (sic): You can activate the option ‘Reply button invokes mailing list reply’ so that replying to a mailing list message just does the ‘right thing’ without need the specific Mailing List submenu items.

    Spam: You don’t have to install SpamAssassin on your machine, the SA plugin can communicate with a remote SA. Yes, SA is a bit slow, bogofilter is quicker and just as effective once it has been well trained.

    Reading Email: you don’t need a plugin to be able to read HTML mail. The option ‘Render HTML messages as text’ will strip the tags from the html and display it as plaintext, respecting linebreaks and stuff.

    You didn’t even mention the powerful Actions feature, which opens up many possibilities!

  • Howard

    What about RSS? Handling RSS in Thunderbird seems much more natural than using a web browser and is my preferred method of reading RSS. Does Claws Mail handle that?

  • Peter

    I don’t remember with the version I used to compare but version 3.5 has a plugin that will give you the option to create an account to be used for RSS.
    Personally I don’t use it, I prefer a separate reader.

  • Hi Guys,

    I am Claws-mail – email client user . Version I use is : version 3.6.1 on gentoo.

    I am very much satisfied with the way claws-mail works for me – i use GPG and calender mostly. It is very fast. I have some issues with claws-mail –

    1. vcalender plugin is not as good as thunderbird may be. does not show a sidepanel like the calender in thunderbird shows – don’t like vcalender plugin much.. can not import other calenders like my gmail calender.

    2. I find it extremely annoying when I receive an email with html format or a doc attachment in it. It takes forever for claws-mail to download that email- eventually I have to kill claws-mail client and check that email on web interface for our email server. I delete that email from web interface because then if I re open claws-mail client it again takes forever to do anything with client, client is open but keeps on working on that email forever and I can not even browse through other folders or stop anything. I kill it.

    I wonder if other users of claws-mail also have this issue..

    Installed versions: 3.6.1(21:10:47 11/12/08)(crypt dillo doc gnome imap ldap session spell ssl xface -bogofilter -gnutls -ipv6 -kde -nntp -pda -spamassassin -startup-notification)


  • Peter

    I run Claws in Ubuntu but I don’t experience any of the HTML problems you describe.
    Which plugins are you running?

  • Using dillo to show html emails. I am on amd64 and claws-mail is 64bit, GTK+ 2.14.4 / GLib 2.18.2
    Locale: C (charset: US-ASCII)
    Operating System: Linux 2.6.27-gentoo-r1 (x86_64)

    I also have this problem when someone send email with .doc attachments

    • Partho Banerjee

      I use a plugin called fancy. Available at claws mail website. Never had any HTML message display issue.

  • Thanks for this comparison, i’ve been thinking on switching from thunderbird to claws mail. But i have one question, do you know any tools to move all messages from thunderbird into Claws Mail(if there’s any)? because that’s what that keeps holding me back from switching to another email client

  • Peter

    Claws mail can import mbox which is the format Thunderbird stores its email

  • Thanks for the reply, i thought i need to use the python script found at 😀

  • Greg

    The main reason for me to switch from thunderbird to claws was the ability to filter against the adressbook, and templates (per folder). I’ve seen both features only in The Bat! before. I was missing them since I moved to Linux and thunderbird.

  • alpha1

    I installed CLAWS E-mail on my eeePC laptop running Kubuntu Jaunty, but could not figure out how to import all of my Thunderbird E-mail and settings. Is there some way to do this>

  • Thanks 4 the comparison.

    I used Thunderbird for several years and then switched to Claws a year or so back (mainly for the GPG support. Now I’m thinking of switching back to Thunderbird because:
    Claws won’t let me do anything else in Claws when it’s checking e-mail accounts.
    Claws won’t even let me xkill it when it’s off checking for mail!!
    I’m getting some (html) e-mails which show nothing in claws unless I invoke html viewing
    I don’t like the way Thunderbird handles multiple SMTP accounts
    I don’t like the way Claws Mail handles multiple SMTP accounts

    Perhaps I should try to run The Bat! in wine?

    I used The Bat! for several yease and was quite happy with it. It’s a pity that the thunderbird (& Claws) developers don’t do SWAT analysis of their product and the competition (from the users’ perspective, NOT the programmers,) to bring in some of the features which work in The Bat! (But The Bat! is not enough to get me to go back to W).

    • The inability to do anything Claws when it is checking mail is annoying.
      I don’t have the problem of multiple SMTP accounts although I do have several accounts that require different SMTP accounts. I “solved” it by setting up a mail server in my local network and have the mail server handle the remote SMTP settings, In claws I just have on SMTP setting, to my local mail server.

      I never used The Bat!, but I don’t like to use wine in general, kinda defeats the purpose of running Linux.

  • Wine leaves lots to be desired but The Bat! does have lots of good points (IMAP is not one of them). I had thought of having my own mailserver locally but that seems to me to be overkill for something which SHOULD be quite simple – getting the mail!!

    I have given up on Claws (for a while anyway) an have decided to use The Bat! (under wine) for the pop3 accounts and Thunderbird for the IMAP. It’s a compromise but one I can live with as I can e-mail between the accounts for the few times when I need to transfer info between the clients.

    Thanks for your thoughts.

  • Nikkobuntu

    Thank’s all for the topic …

    I was on finding an alternative to Thunderbirb, mainly for the poorly way that Thunderbird is managing contacts. On one of my PC’s I switched to Evolution .. and not really happy with it, but it’s not the topic here.
    SO, what about the contact management offered by Claws ?
    Is any one who had experience with Outlook or Evolution would give me some commentary on this point ?

    Thks in advance ..

    • Thunderbird + Zindus extension = Thunderbird + GMail Contacts sync

  • Bogdan

    This is a very old thread. However, I gave a pass through everyone’s comments and I noticed that no one had emphasised the MAJOR flaw Thunderbird has and why I will never use it: it can handle only mbox format, which it means that ALL the messages are included in a SINGLE file. Imagine that yo need to search through such a mess. It is true that the re are some index files that speedup the search, but it has a single point of failure the unique mbox file. On the other hand claws supports MH format which has on message per file like maildir has (the only linux mailer supporting maildir is kmail, but the latest version is so bloated and slow that makes it unusable)

    When you have a mail archive with hundreds of thousands of emails from the last 15 years as I have you don’t want to use thunderbird

    • Bogdan

      I forgot to mention that I had once a MBOX file corruption and it took me days to restore it. I will never use MBOX again. The solution is “maildir” and MH. I like maildir better but the lack of a good supporting client made me switch to claws mail. At the beginning i found the interface awkward especially the search functions, but I got used to it and I am happy with it.

  • Selador

    I have used claws for years.

    I am switching over to thunderbird out of frustration.

    I don’t require and don’t ask for full html support, or all of the visual candy, gimcrackery, and bowwhistles that a lot of people want. So I have gotten along fine with the limitations that claws has in this area.

    But about a year ago, I started wishing that I had just the three basic simple ‘extras’ that most text eidtors out there have. Bold, Italic, and underline. I’m not even asking for smilies. Just the basic three.

    Apparently that is tantamount to asking that I be allowed to chew the head off of someone’s babby kitten, if you ask the people at claws!

    So, after a year of trying, and being treated like a leper and worse, for trying… I am giving up and switching over to TB.

  • Jawondo

    Using the ‘Net should not require the average user to become an expert; following certain thing are just too difficult, and the true experts take them for granted, forgetting its about the “ordinary folks” !
    My question : is that account you open when you start claws mail just like
    an ordinary simple e-mail provider e-mail account? In other words, can I use it
    as my only, or main e-mail account, thereafter, even if I have no retrieval of other outside accounts to perform….? Thanks for a clear response, and not a show-off
    of Internet savvy and technical knowledge.