if u did "/downloads/qmailrocks/scripts/qmail_patches.script" at
http://www.qmailrocks.org/qmail.htm . this means u have smtp auth.
try to telnet your server, and try to send email outside domain. (not your domain)
[root@linux root]# telnet 212.x.x.x 25
Trying 212.x.x.x...
Connected to 212.x.x.x.
Escape character is '^]'.
220 mail.domain.com ESMTP
mail from:maxut@domain.com
250 ok
rcpt to:maxut@yahoo.com
553 sorry, that domain isn't in my list of allowed rcpthosts (#5.7.1)
if u get this error u have smtp auth.
if u dont have smtp auth. u must patch qmail source with smtp auth and compile it again. it is not necessary to install other packets again.