There is an article posted where a fellow (who goes by "Computer Bob") had some bad experiences with KMail and declares to the world that "this KMail problem makes Linux look bad". Well, I'm not here to dispute the problems he had. I WILL dispute though that KMail is the same as "Linux".
You see, Linux is made up of THOUSANDS of software packages. KMail happens to be one of thousands of pacakges on a typical KDE based desktop. KDE itself contains a large number of software packages. To make the claim that a "KMail problem makes Linux look bad" is like saying "this one blade of grass looks different and wreaks the entire golf course".
ComputerBob even says it himself - Linux (and open source) is about choice. We can choose what software packages we want to use, or not use. We can change those software packages to meet our needs, if we wanted to. But he misses the clearly obvious rebuttal to his article - he is free to choose NOT to use KMail. The developers are free to ignore his complaints.
Now, if KMail *does* have a problem with a) initial setup of an outgoing mail server, or b) converting HTML email to plain text when replying to that email, then the developers need to make a choice whether or not to fix it. The first issue sounds like a bug that *should* be addressed. The second issue sounds like a project goal thing. If it is KMail's goal to be "the" email client for all KDE users, and allow easy conversion of Windows users, then this issue needs to be resolved. If however, KMail's goal is to be a developer's email client, then perhaps HTML email (and all the issues that go along with it) is not a high priority. But, the point is that ComputerBob looked at KMail for HIS specific needs. This HTML issues obviously means that KMail does not meet his needs. Done deal - find a different email client ComputerBob. OR, if he were really intent on this, he *could* grab the source code, and fix it. The only other option is to talk (politely) to the developers, and make a case for this change. But again, the developers are free to choose to talk with him, or not.
For me, I have never encountered the problems that ComputerBob has. Because a) I have a tech background and have an intuitive understanding of email clients (which means an SMTP connection issue has an obvious fix for me), and b) I don't use HTML mail. I don't use HTML because, for me, it is too great of a security risk. HTML can be crafted to get external images/resources, which means people can track when I read their emails. OR an embedded object could be used to attempt to compromise my system. I prefer my security and privacy, and so use text only email. But I also realize that's not the right answer for everyone.
Now the kicker. I abandonded KMail a couple years ago, but for totally different reasons. For me it was IMAP access. I prefer to use IMAP for my email so that I can view the same mail even when I'm on the road. As long as I can connect to the server, all my email is available to me. KMail does support IMAP.
So, if KMail does support IMAP, and I'm choosing IMAP, what's the problem? Well, add some large directories. I have some folder that receive hundreds of messages a week. I also tend to not delete my emails - I never know when I'll need to reference them again. I do get rid of obvious junk though. But this means that my folders accumulate a large number of messages. KMail had problems dealing with these sizes. It DID handle it, but it wants to "refresh" the directory listing on a regular basis, which means noticable delays in using KMail. The delays were *just* over my tolerance level, so I switched to Thunderbird which doesn't have these delays.
Freedom of choice prevails again, AND a little subjective thinking. I had the choice to move my email to a different client. My emails were not stored in a proprietary format (think .pst files), and I was not hindered in moving to another email client. (THIS is why I do not support Microsoft file formats!). In terms of subjective thinking, I realized that KMail just didn't meet my needs, and found something that did. But I didn't complain that I had to do sooooooo much work and effort. It's a cut and dry issue for me - Does it do the job? No. Ok, so what are the alternatives. Repeat until I find something that DOES do the job.
Now to be fair to KMail, I made my choice to move to Thunderbird about 2 years ago. I have not seriously looked at KMail again since then, so the issues that prompted my move may have been dealt with. One day I'll have some spare time and will take another look.
KMail is a good solid email client for anyone running the KDE desktop. It is suitable for a great number of people. But you'll have to try it yourself to see if it is suitable for you. If it isn't, then Open Source has some alternatives for you.