Changes have been made in Git for this ticket:

Bug #10453: Ignore unknown authentication methods; otherwise, they 
give false positive when authenticating

  3 files changed, 11 insertions(+), 5 deletions(-)
http://git.horde.org/horde-git/-/commit/8a74526ed0307e61a4e3b4f3ff0d3114c059d87b

I update my IMP with Bugfix from Ticket 10450 thank you now i can see 
the mails.

But i cannot understand why i can login with wrong userinfo or password.
I activate logging in horde to get the following info:

2011-08-24T10:04:21+02:00 NOTICE: HORDE [imp] Login success for m333h 
(Horde user m333h) [192.168.1.174] to {91.194.132.21:110 [pop]} [pid 
27165 on line 179 of "/www/php/horde/imp/lib/Auth.php"]

? a parsing error? after the [-err] [quit] the imp client sees the 
[ok] response?

------------------------------
S (1314173046,3): +OK Hello there.
C (1314173046,3): CAPA
S (1314173046,43): +OK Here's what I can do:
S (1314173046,43): SASL PLAIN LOGIN CRAM-MD5 CRAM-SHA1 CRAM-SHA256
S (1314173046,43): TOP
S (1314173046,43): USER
S (1314173046,43): LOGIN-DELAY 10
S (1314173046,43): PIPELINING
S (1314173046,43): UIDL
S (1314173046,43): IMPLEMENTATION Courier Mail Server
S (1314173046,43): .
C (1314173046,43): [AUTH PLAIN Command - username: m333h]
S (1314173051,5): -ERR Authentication failed.
C (1314173051,5): AUTH LOGIN
S (1314173051,58): + VXNlcm5hbWU6
C (1314173051,58): bTMzM2g=
S (1314173051,63): + UGFzc3dvcmQ6
C (1314173051,63): [AUTH LOGIN Command - password]
S (1314173056,68): -ERR Authentication failed.
C (1314173056,68): AUTH CRAM-MD5
S (1314173056,7): + PENGRkIyMjZGNjRCOEVCQ0QwODg3Nzc1MzA5RTdBRDMyQG1haWwyMT4=
C (1314173056,7): [CRAM-MD5 Response]
S (1314173061,76): -ERR Authentication failed.
C (1314173061,79): QUIT
S (1314173061,83): +OK Better luck next time.
------------------------------
S (1314173062,24): +OK Hello there.
C (1314173062,24): STAT
S (1314173062,27): -ERR Invalid command.
C (1314173062,27): STAT
S (1314173062,32): -ERR Invalid command.
C (1314173062,33): STAT
S (1314173062,35): -ERR Invalid command.
C (1314173062,38): QUIT
S (1314173062,4): +OK Better luck next time.

My Configuration:
Authentification:
$conf['auth']['admins'] = array('test@example.com');
$conf['auth']['checkip'] = true;
$conf['auth']['checkbrowser'] = true;
$conf['auth']['alternate_login'] = false;
$conf['auth']['redirect_on_logout'] = false;
$conf['auth']['list_users'] = 'input';
$conf['auth']['params']['app'] = 'imp';
$conf['auth']['driver'] = 'application';

backend in imp is pop3

if i try the same with the imap backend it works