XFOR: NDR with Error 501 Syntactically Invalid HELO Argument(s)

• Microsoft Exchange Server, versions 5.0, 5.5

SYMPTOMS

When sending e-mail to a third-party SMTP server or through a firewall, a non-delivery report (NDR) similar to the following may be generated:

Subject: Notification: Outbound Mail Failure - A protocol error occurred.

A mail message was not sent due to a protocol error.

501 syntactically invalid HELO argument(s)

The message that caused this notification was:

CAUSE

This error is generated by a third-party SMTP server or firewall.

When the Microsoft Exchange Internet Mail Service establishes a connection to a remote host, the Internet Mail Service initiates the SMTP conversation with "EHLO domainname.com". If an error is returned, the Internet Mail Service falls back to "HELO domainname.com". If the HELO command returns an error, an NDR is generated containing the error.

Additional query words:

Keywords : exc5 exc55
Version : winnt:5.0,5.5
Platform : winnt
Issue type : kbprb