Hi all, I m using MS Exchange 5.5. this is working fine but while i m send a mail to a perticuler domain i m getting NDR , i can receive mail from there . This is for all the user of this particuler domain. Pls anybody can suggest me the cause? Thanks msg is like that:------- The following recipient(s) could not be reached: 'osama al hasan' on 9/24/2002 3:17 PM Unable to deliver the message due to a communications failure The MTS-ID of the original message is: c=US;a= ;p=CUPOLA;l=SERVER01-020924111625Z-32359 MSEXCH:IMS:CUPOLA:CTSL:SERVER01 3503 (000B09AA) 503 please introduce yourself, first