Unsolicited Commercial Email consulting

Unsolicited Commercial Email consulting, or spam (as it has become more commonly known) seems to be with us to stay, in much the same way as the junk mail that lands on our doormat each morning. Most of the time we happily delete the daily tide of junk email that arrives in our inbox without giving much thought as to where it might have come from, or how it made its way to us. The fact is that each message must have started its brief life on a server somewhere, and unfortunately spammers rarely go to the trouble of providing their own server hardware, preferring instead to use other people's. Quite possibly yours.

It might seem strange that someone else could use you server to send email without even having a mailbox on your server, but there is nothing in the SMTP specification that specifically forbids this. Presumably, in the days when email was first conceived no-one thought it likely that anyone would want to take advantage of someone else's equipment in this way. In this day and age it is quite apparent that they do. In fact an entire industry, based on just this concept, seems to be developing quite rapidly.

So how do you know if it is possible for someone to use your server in this way? Very often the first thing you will know about it is a message from somebody like ORDB, ORBZ or Spamcop arriving in your Administrator Inbox telling you that your server is behaving as an open relay. This could quite possibly mean that someone has received some junk mail and was sufficiently provoked to find out it's source (i.e. your Exchange server) and submit the IP address for testing. Not only is this rather embarrasing, but it could mean that some of your emails will no longer reach the intended recipients, since some organizations refuse to accept emails originating from sources known to be open relays.

Fortunately, you can easily find out for yourself if your server is open to relaying. Then you can do something about it. Procedure

The first thing you need to do is to find out if it is possible for someone to relay a message through your server. One way of doing this is from a telnet session to your Exchange server on port 25, which is the port used by the SMTP service. If you are testing from an MS Windows computer, type telnet in the Start menu and open a session as shown in figure 1. Of course, you'll need to supply the name of your own server instead of 'SRVR-1'.

Your version of the telnet may well look different to this, but they are all basically the same. It will make things much easier if you make sure that local echo is enabled, otherwise you won't be able to see what you are typing. Do this by selecting the appropriate menu option or (if you are using the CLI version) by typing in set local_echo.

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