Disable EHLO in Exchange 5.5 and Exchange 2000

Posted On 2007-05-03 by FortyPoundHead
Keywords: XADMIN Exchange Greeting EHLO HELO Disable SMTP
Tags: Exchange 
Views: 1939

EHLO (Extended Hello) messages are sent by Microsoft Exchange 5.5 and 2000 by default when starting an ESMTP conversation with another server. There are a few, although not many, servers that cannot handle ESMTP for inbound messages and can only accept mail sent via standard SMTP. A server that cannot handle EHLO will generally respond with a 550 error message with the descriptor "Unknown command" when the EHLO is sent.

If you are administering an Exchange server and you find that you cannot send mail to a given domain because of this problem, it is possible to set Exchange to send mail using HELO (standard SMTP) rather then EHLO (ESMTP).

To disable EHLO and re-enable global HELO, follow these steps:

For Exchange 5.5:

In the Registry, find

and add the REG_DWORD value DisableOutboundESMTP. Set it to 1.

Close the Registry Editor and restart the Internet Mail Service.
For Exchange 2000:

Create a new SMTP connector.
In Exchange System Manager, right-click on the new SMTP connector and select Properties | Advanced.
Select "Send HELO Instead Of EHLO".
Click OK.
On the whole, however, this should not be viewed as a permanent solution, since a mail server that cannot gracefully reject an EHLO message is either misconfigured or out of date. If you are experiencing problems with one specific mail server, contact the administrator of the server and learn what you can about their configuration.

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