Openwebmail can't send mail
 

I am using Rh 8.0 and postfix 1.1.11-5. I can use outlook express to receive and send e-mail.
I don't know why i can't send mail from openwebmail and i don't know why the user name of
postfix alias name is yung: kelper. When i use "kelper" to login to openwebmail. It doesn't change to
my alias name "yung" How can i configure it ?
THX


Openwebmail Error
Sorry, there was a problem sending your message. Please click your browser's Back button, check your message, and try again.!

The error is shown below:

<<< 220 yung.no-ip.biz ESMTP Postfix
>>> EHLO yung.no-ip.biz
<<< 250-yung.no-ip.biz
<<< 250-PIPELINING
<<< 250-SIZE 10240000
<<< 250-VRFY
<<< 250-ETRN
<<< 250-XVERP
<<< 250 8BITMIME
>>> MAIL FROM:<yung@yung.no-ip.biz>
<<< 250 Ok
>>> RCPT TO:<abc@abc.com>
<<< 554 <abc@abc.com>: Recipient address rejected: Relay access denied
>>> RSET
<<< 250 Ok
>>> QUIT
<<< 221 Bye

Can anyone help me ????????

help me please