[Kroupware] postfix error log

[Muhammad Reza]

dear All,

My Korupware installation on RH-9.0 work fine, but i have problem with 
Postfix MTA. I'll tried to send email message to  user at domain.com  
(already add  via webadmin interface and domain is already in relayhost 
at postfix main.cf.template). but Postfix always failed with this error log
 
postfix/qmgr[10204]: warning: connect to transport relay: Connection refused

the postfix/main.cf and master.cf are default, with extra domain in 
relayhost.

can someone give clue ? any help will be appriciate.
On second though, why Kolab didnt add domain relayhost automatically 
when i'm add user at domain.com via webadmin interface ?

regards
Reza