We have an Exchange Server (2010) on site that sends our mail to the world using MX(DNS) records. When I look at the queue, several domains have 421 4.4.2 Connection dropped due to ConnectionReset. I've telnet into the SMTP port of the servers refusing connection and doing HELO or EHLO (domain) always returns Syntax error the first time it is submitted. The second time the receiving server replies to the command. Once I get the HELO or EHLO command to be received it takes all other commands as normal.
220 smtp-gateway2.carleton.ca ESMTP Service ready EHLO **********.ca 500 Syntax error, command unrecognized EHLO **********.ca 250-Requested mail action okay, completed 250-8BITMIME 250-SIZE 20480000 250-ETRN 250-STARTTLS 250 OK
No backspaces or any other keystrokes besides what you see. I'm using our domain name that would be sending the email in the sample above.
Could this be the reason I am seeing the 4.4.2 error in our send queue? If so what would be causing this issue?
To telnet I'm using putty from our Exchange Server.
Extra information: Web traffic for our company uses a different public IP than our Exchange server uses for mail/smtp. All information from Exchange that uses port 25 is forcefully being re-written to the correct public IP by the Firewall. There was an issue with mail having the incorrect public IP and being rejected because there is no rDNS for the web traffic IP.