achine, not on some distant computer which runs a shell account), but I still recommend that you will get a shell account at nether.net (in fact they teach you a lot of great Unix-newbies stuff when you sign up).Note about Telneting from Macintosh: Macintosh does not come with a Telnet program. However, you can download one from: http://www.ncsa.uiuc.edu/SDG/Software/MacTelnet/ (thanks to little_v for this one!).Now, let's see what we get after we telnet(19) to mailgw.someone.com:25 (in this case, the character : stands for 'on port', so mailgw.someone.com:25 means mailgw.someone.com on port 25).220 alpha.someone.com ESMTP Sendmail 8.9.3/8.8.6; Thu, 8 Jul 1999 21:46:04 +0000 (GMT).AHA! This is... this is... ugh... WHAT THE HELL IS THIS THING?!This, my friends, is a daemon banner(4), and it just gave us tons of valuable pieces of information!Normally, this info is intended for a client program(16) to determine what version of Sendmail the target is running and how to communicate with it (the program should know that, for example, every Sendmail version below 7.0.0 uses the command 'halb' instead of the command 'blah', etc').This daemon banner thing is also great for hackers and crackers, since we can determine what version our target is running. Later, when we will discuss about how to actually hack the server, this data would be EXTREMELY valuable.Okay, let's analyze what we've got...220... we don't know what this is right now...alpha.someone.com... no luck, can't make anything out of it so far...ESMTP... hmm... SMTP stands for Simple Mail Transfer Protocol. It is the protocol(18) used by email clients to communicate with Sendmail daemons, and this is what we're trying to learn right now. ESMTP is Extended SMTP. It's the same as SMTP, only it contains some more commands. Let's leave this alone for the time being.Sendmail 8.9.3/8.8.6 - AHA! There's something interesting. We got the version of the Sendmail daemon! Remember this, it will h...
