There is a mail server that I'm trying to test using telnet. I telnet to the server on the port and it responses with "220 **************************************************************************"
The server is exchange and sending of mail requires authentication.
When I enter the command "helo" I get "500 5.3.3 Unrecognized command"
no matter what I enter, even "quit" I get the same response. The website MXToolbox (http://mxtoolbox.com/diagnostic.aspx) says that the mail server is responding properly.
What could be wrong?
Best Answer
If the response truly is
then the answer is that, contrary to what you might think, you are not talking to a Microsoft Exchange SMTP server.Rather, you're talking to a Cisco router with the "mailguard" mechanism enabled, as Microsoft explains to those who think that they have Exchange problems. As Cisco says, if you want to talk to a Microsoft Exchange server — or to any other server that requires SMTP extensions such as SMTP AUTH, for that matter — you must disable the "mailguard" mechanism and let the world talk to your actual server.