authentication failure: cross-realm

[JOYDEEP]

Dear list,

Here is the config I had with working cyrus

/etc/imapd.conf
-----------------------
servername: lvps87-230-8-228.dedicated.hosteurope.de
defaultdomain: dedicated.hosteurope.de
loginrealms:  dedicated.hosteurope.de
-----------------------

here is the change I have done after getting a DNS pointing to my email
server
-------------------------------------
servername : opendingo.com
defaultdomain:   opendingo.com
loginrealms:   opendingo.com
-----------------------------------------

but now "cyradm -u cyrus localhost"  says
login relams fail.

can anyone have any idea of this problem ?