Telneting to Port 25

In this example, I will take you through how I was able to guess what "Eddie Davidson's" email address was at flock.mwci.net. This same technique can be used to verify that email addresses such as: root, postmaster, etc exist at the site.

Briefly, you telnet to the mail port (25) of the host machine and then use the "vrfy" (Verify) command to check email addresses. The format of the vrfy command is: vrfy address.

telnet flock.mwci.net 25 (telnet to the SMTP mail port of the machine)
220-flock.mwci.net Sendmail 8.6.12/8.6.9 ready at Tue, 3 Sep 1996 03:44:45 -0500
220 ESMTP spoken here
vrfy davidson (See if there is an email address with his last name)
550 davidson... User unknown (Nope...)
vrfy eddie (See if there is an email address with his first name)
250 <eddie@flock.mwci.net> (Bingo!)
quit
Connection closed

Figure 3: Telnet Session to Port 25

You may prefer to do this before sending complaint mail to an email address in order to avoid having it bounce back to you with an "unknown email recipient" message

Last modified Sept 23, 1998