ESS:SendFailedException 554 Invalid Address Access is denied

Hi,
I wanted to connect to the blackberry ESS from my email account. we are not having any corporate exchange server for maintaining blackberries. Its a simple account with username and password and i entered in the incoming and ougoing addresses of the connected mode of the blackberry ESS.
The thing is incomig mail is working well. But, while i am sending any message to the same domain or outside of the domain, its showing the message that "SendFailedException 554..............Invalid Address...................Access is denied".
May i know the problem related to this exception.

Thanks,
G.S.Rajasekhar