Hi all, ever since I moved SBS with Exchange into the LAN segment only I have intermittent email NDR's from certain recipients. Now the ISA FW publishes to this secureNAT email server and all mail goes out 100%. However, some of the mail bounces back to original recipient on a reply. I have tried HELO instead of EHELO to no avail, here is a snipit from the NDR. Slightly changed only to provide anonymity ----- Forwarded message from Mail Delivery System <Mailer-Daemon@.SYNTAX-ERROR.> ----- Date: Mon, 27 Jan 2003 12:51:36 -0800 From: Mail Delivery System <Mailer-Daemon@.SYNTAX-ERROR.> Reply-To: Mail Delivery System <Mailer-Daemon@.SYNTAX-ERROR.> Subject: Mail delivery failed: returning message to sender To: kuser@xxxxxx This message was created automatically by mail delivery software (Exim). A message that you sent could not be delivered to one or more of its recipients. This is a permanent error. The following address(es) failed: ruser@xxxxxxxxxxxxxxx SMTP error from remote mailer after end of data: host mail. companyname.net [xx.xxx.xx.25]: 500 5.3.3 Unrecognized command Any help would be appreciated, thanks a million. Peter