Hello,
i have an account on IMAP server (dovecot) and created a few subdirectories under the INBOX directory. After installing kmail a see only INBOX dir on list, all subdirs are not shown. But when i try to sing to the directories - all subdirectories are listed and checked… but do not appear in main window list.
I use dovecot too. I remember having at the beginning the problem you mention until I started using the dbox format.
You have some info about dovecot (probably you already know most of that, but just in case) in this thread, starting from the post #20. If you are interested in dbox format and need help, post again. I use it and I found it easy to set.
I’m not an administrator of IMAP server… I’m a client 
Evolution, thunderbird and others work fine, and kmail doesn’t ((
I’m sorry that I cannot help you.
I suppose it is something in kmail, because I had the same problems with subdirectories until I changed format. And in fact, it worked fine with evolution and thunderbird.
OK, thanks… And how do you think, which client is better to use in KDE? Evolution and thunderbird will load Gnome libs, i don’t want it (
Sorry for the delay.
I have used kmail since first I started with linux. Just for some months I used evolution. I liked some features, but in the whole I prefer kmail by far. I gave a try to thunderbird too. But again, I prefer kmail.
The only problem I have had with kmail is the one you mention about subfolders. I resolved it -as I said before- changing the format in dovecot server.
So, my advice would be kmail, but I understand that you, not being able to change the format in dovecot, are not quite happy with it.
Take a look at this thread. In the first 9 posts there are a lot of ideas. Then it became focused in dovecot imap server.