I am having a problem with kmail, here is the setup- I am running Kubuntu
Fiesty on a new harddrive I replaced. I was previously running Kubuntu edgy.
After I installed the new harddrive and installed the OS I rsync'd my home
directory to restore my previous settings. Everything appeared OK in Kmail,
my email directories and contacts where all there and my account settings
where intact. I hit the manual check mail option and the info line at the
bottom reads "(correct time) transmission complete. no new messages." So I
went to the server VIA web browser and there are messages on the server. Next
I let some time go by to see if that made any difference and it did not. Next
I removed and reinstalled the accounts to see if that was scrambled in the
transfer, still the same problem. Through all of this I have not received any
error messages or password requests from the server and the sendmail has
worked all along. So I am a little stumped, all the settings are in order, it
has comm with the server but it is not fetching messages from either of the
servers (2 accounts set up) yet I can send on either account.
So I have to assume I am missing something pretty obvious or there is a bug?
Any suggestions?

If your mail server is the common POP3 type you should be able to talk to it directly as described in http://communication.howstuffworks.com/email1.htm .

Just run

telnet <name of pop-server> 110

and issue commands to log in and list your messages. You may be able to verify your settings and isolate the problem to kmail or elsewhere. Like the article says, it is a simple protocol, so odds would be on a config error rather than a program bug.

Check your messages first, in case you accidentally delete them while playing with the server.

kmail's indexes are probably in a muddle. You need to re-create them:

Make sure kmail is not running.
Locate your Mail directory. For dapper it is in ~.kde/share/apps/kmail/mail
Delete all the files there taht are called *.index *.index.ids and *.index.sorted
Restart kmail, it may be slow to start as it is re-creating the indexes.
It should now work properly.

shredi - did you find a fix for the problem you reported with kmail and pop? I have found exactly the problem you describe (with Feisty also), except with a brand new installation.
I can use getmail to fetch the emails, but using kmail I just get the "transmission complete. no new messages".