pop3 or imap logon failure

Hi, I try to configure Pop3 to be used by some user but it was not successfull.

I have 1 CAS sever and 2 MBX in dag mode.

When I try to connect to pop3 with Telnet casserver 110

I always get login error.

I active pop3 logging for debugging and here is the results in the log file

-ERR Logon failure: unknown user name or bad password."";Msg=Proxy:A-exchmbx-02.CRL.int:9955:SSL;ErrMsg=ProxyNotAuthenticated"

I try the login with

DOMAIN\user

user

user@upnsuffix

Nothing works.

I follow all the doc to enable pop and backend, internalconnectionsettings, external... All the good port is open in firewall.

What can be the problem?