Version: (using KDE 4.1.4) kmail duplicates a lot of code already written. It has code for POP3, imap, ssl/tls auth, etc., which are already present in apps like fetchmail, procmail, offlineimap, etc., which are used widely and tested heavily. kmail should follow the UNIX tradition of 'do one thing and do it right' by using these programs and presenting a nice UI around them. We have a lot of complaints with kmail like it eating mail, crashing when / gets full (and deleting mail in the process) and so on. I had switched to kmail about 5 years back but have recently migrated to fetchmail/offlineimap + mutt because I just couldn't trust my mail to not get damaged or lost.
There are things that can not be done in an easy way calling external processes (that also have bugs), and do not support D-Bus like, for example, the akonadi integration (http://pim.kde.org/akonadi/). KMail is doing only one thing (managing mail), and is doing it quite good, progressing a lot with every new version. But feel free to create a GUI for the external tools (for example with PyKDE).
I kind of expected such a response. However, please give it some thought, if you can. KMail is notorious for losing mail (a few bugs were fixed for 4.1.4, IIRC. They existed since 4.1.1). The 'mail lost when / is full' bug I think has been open for a good 4-5 years now. It's just not possible to trust a software with such dubious track record. If, instead, the kmail team could work on fetchmail to fix bugs they find there and use it, it'll be a better accomplishment for the entire OSS community. Also, the fetchmail people know more and better about handling mail and implementing RFCs than KDE people, whom I know of making some great UI. I've been a KDE user and supporter for well over 9 years now and it really hurts me to move away from "KDE programs" to do things to others, but I have been regularly going back to software which I know will work. Eventually, it would just seem that I use KDE just to login and then use anything but KDE.
* We are working to solve ALL of the out-of-space bugs in kde 4.3. * The integration with sendmail is already done as an sending agent. * For procmail or other receiving mail agents, if they save the mail in mbox format or maildir format, kmail can be used to read them. What kmail actually is not able to do is to call them periodically to retrieve new mail.
The problem with this is that fixes in KDE don't get backported to stable versions (eg, 4.2, 4.1..) and only go into newer releases, like 4.3 as you mention. Distributions wouldn't bother about backporting as well. So if someone's using 4.1 or 4.2 (or even 3.5, for you-know-what), they're stuck with the problem for ages while the KDE team can hand-wave saying it's been fixed. It's much more simpler to maintain a smaller, leaner code base and reusing existing code than to just inconvenience the users while pretending to own every inch of the software space. Might sound harsh, but I've said it with good intentions and after years of supporting KDE and having been meted out with such treatment several times.
If the patch for a problem in 4.3 does not breaks things in a previous branch, it is usually backported to the previous stable branch (4.2.1 or 4.2.2, depending on the time it is applied). Therefore, distributions backport them. :-) Would you force Linus to backport a lot of the new things from linux 2.6 to linux 2,4 or even linux 1.x? No, but this is the strength of FOSS, you or someone else could do it. The same happens with KDE. But someone has to do it, and it will not be done by the KDE developers, as they are working to improve the KDE experience, based on the KDE4 sourcecode.
I don't think you understand. "Something new" does not equal "major bugfix". Also, my original point is, why doesn't kmail/kde stick to doing UI and use well-established software for the purpose they were written? Can you tell me that my existing 3.5 installation will get the '/ is full' bugfix? I can tell you with all certainty that it will not. That's how I've known KDE to work.
«kmail should use fetchmail, procmail, sendmail, etc programs for fetching mail» That won't happen. The future for KMail is called Akonadi and there's no plan to use one of those external programs.