Version:           1.13.2 (using KDE 4.4.2) 
OS:                Linux

One of my mail accounts is at GMX and I use POP3 to fetch the mails.
I use TLS encryption for that. The authentication (KMail calls it "Anmeldeverfahren" in German) was set to - well I don't know exactly, maybe CRAM-MD5 but definitely something other than "Plain text".
I was already wondering why there was no new mail there, and eventually I checked.
There was, plenty of it! But KMail seemed to be fetching without problems and claimed "No new messages". (Exact German message is "Übertragung für Konto GMX abgeschlossen. Keine neuen Nachrichten.") This is clearly a severe misinformation! If there is any problem, a popup must come.
I reviewed the settings of this account and decided to check the security features. Pressing the button to test what types of authentication the server supports, I found out that GMX must have changed what they support, leaving the authentication I used unsupported. I'm now using "Plain text" and mail is fetched fine again.

Reproducible: Didn't try

Steps to Reproduce:
I'd need to have new mail at GMX to reproduce it, so haven't tried.
It should be enough to take a POP3 mailbox and set the authentication to something the server doesn't support.
Maybe it only happens with one specific type of authentication.

Actual Results:  
No mail fetched, no error message.

Expected Results:  
Any problem while fetching mails must result in an error message (popup).

OS: Linux (x86_64) release 2.6.32-22-generic
Compiler: cc