Version:           1.9.5 (using KDE KDE 3.5.5)
Installed from:    Debian testing/unstable Packages
OS:                Linux

(noticed with KMail 1.9.4, but tested with 1.9.5 too)

1. Configure a POP3 account with TLS and DIGEST-MD5 auth.
2. Try to login and download mails.

Sometimes (!!! yes, not always, but sometimes, I know it's weird) KMail sends wrong QoP attribute, and confuses pop3 servers.

Here is a log entry from dovecot pop3d:
15:49:55 Info: auth(default): digest-md5(?,<rip>): Unknown QoP value: pop

This only happens with TLS turned on. If I turn off TLS then the authentication always succeeds.

Here is the thread which I've started on the dovecot mailing list:
http://www.dovecot.org/list/dovecot/2006-October/016829.html

But I'm going to quote here some notable lines:

Timo:
"[...] what it means is that Dovecot announces that it supports "auth" QoP (Quality of Protection). KMail is supposed to reply back that it wants to use "auth" QoP, but it replies with something else. [...]"

Then Timo (dovecot's author) made a patch which shows what QoP has been sent by KMail.

Me:
"Using the latest cvs (with the above patch):

15:49:55 Info: auth(default): digest-md5(?,<rip>): Unknown QoP value: pop"

So it seems that KMail sometimes replies with that "pop" QoP which confuses dovecot.