OWA Error-"The message cannot be sent"

Hello,

I installed Microsoft Exchange 2010 on Windows Server 2008.The installation was successfully completed. The URL for the OWA is also working.But there is a problem in sending and receiving emails.The user is unable to send and receive emails.The emails get moved into DRAFTS folder as soon as it is sent and a message "The message has not been sent" is displayed.

Please help me out with the above issue.

Thanks,

Shatadiya Saha