This problem relates to Extended SMTP. ESMTP includes encryption on top of the authentication that Exchange Server uses to transfer Internet Mail. SMTP doesn't include this additional layer of encryption. Some systems aren't compliant with Internet Engineering Task Force (IETF) Request for Comments (RFC) 1651, which defines ESMTP commands; thus, the systems don't accept ESMTP commands. This limitation can result in compatibility problems when sending email over the Internet: The receiving email server expects an SMTP response from the sending email server, and the sending email server sends the response in ESMTP, which the receiving email server doesn't recognize. To solve this problem, you can disable outbound ESMTP in Exchange Server. However, by doing so, you lose the ability to send the ETRN command on a dial-up connection. ETRN is an ESMTP command that alerts one ESMTP gateway or mail host to process email that is waiting delivery to another SMTP mail handling system. If your email server is sending and receiving email over a leased line, this loss of ability won't be a problem. However, if you're using Exchange Server with DUN to retrieve email from an outside host, talk to the host's managers about the potential impact of disabling the ETRN command. Disabling ESMTP also removes the added encryption layer gained by using ESMTP rather than SMTP. To disable outbound ESMTP in Exchange Server, start regedt32, go to the HKEY_LOCAL_MACHINE \SYSTEM \CurrentControlSet \Services \MSExchangeIMC \Parameters subkey, and add the DisableOutbondESMTP subkey of data type REG_DWORD and a value of 1. Verify that the new value appears in the parameters list, close regedt32, and stop and restart the Internet Mail Service (IMS). HTH Piers -----Original Message----- From: Zafar Pravaiz [mailto:pzafar@xxxxxxxxxxx] Sent: 24 September 2002 12:29 To: [ExchangeList] Subject: [exchangelist] NDR for a perticuler domain http://www.MSExchange.org/ 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 ------------------------------------------------------ List Archives: http://www.webelists.com/cgi/lyris.pl?enter=exchangelist Exchange Newsletters: http://www.msexchange.org/pages/newsletter.asp Exchange FAQ: http://www.msexchange.org/pages/larticle.asp?type=FAQ ------------------------------------------------------ ISA Server Resource Site: http://www.isaserver.org Windows Security Resource Site: http://www.windowsecurity.com/ Windows 2000/NT Fax Solutions: http://www.ntfaxfaq.com ------------------------------------------------------ You are currently subscribed to this MSExchange.org Discussion List as: pwhite@xxxxxxxxxxxxxxxxxx To unsubscribe send a blank email to $subst('Email.Unsub')