You can do this yourself if you want. Go set up a yahoo account - we'll call it fake_name@yahoo.com. Log in to your account and go to options. Go to vacation response and type in something you would like to send to someone. A "victim." We'll call them victim@example.com. You can say any nasty (or nice!) things at all you want to this victim, just put it in the vacation response. They won't know it's from you.

Regardless of how well you know how email works, you can follow these steps. You'll need to know how to use telnet. If you're using windows, turn localecho on. Go look it up. Ok, now do this (it might not work on some cable/home connections were outbound port 25 is filtered):

[you type] telnet d.mx.mail.yahoo.com 25
[it  says] 421 Message from (38.103.63.62) temporarily deferred - 4.16.50.  Please refer to http://help.yahoo.com/help/us/mail/defer/defer-06.html

And then it disconnects you. Note that you could use any letter a-g followed by mx.mail.yahoo.com. Now, go have a sandwich. Or pretend you're a spambot and do a tiny little bit of real work before you get back to the spamming business.

Ok, we're back? Has it been about 5 minutes? If not, go have another sandwich. And some chips or something.

K, so now we'll reconnect:

[you type] telnet d.mx.mail.yahoo.com 25
[it  says] 220 mta256.mail.re4.yahoo.com ESMTP YSmtp service ready
[you type] ehlo 38.103.63.62
[it  says] EHLO 38.103.63.62
[it  says] 250-mta256.mail.re4.yahoo.com
[it  says] 250-8BITMIME
[it  says] 250-SIZE 31981568
[it  says] 250 PIPELINING
[you type] MAIL FROM:<victim@example.com>
[it  says] 250 sender <victim@example.com> ok
[you type] RCPT TO:<fake_name@yahoo.com>
[it  says] 250 recipient <fake_name@yahoo.com> ok
[you type] DATA
[it  says] 354 go ahead
[you type] To: fake_name <fake_name@yahoo.com>
[you type] From: victim lastname <victim@example.com>
[you type] Date: Wed, 31 Oct 2007 22:45:59 +0000
[you type] Subject: Ew...
[you type]
[you type] It smells like spiced ham.
[you type] .

Note that there is a blank line after the Subject: line, and the last line is a period (.) on a line by itself.

Yahoo will take what you sent, send it to your fake_name@yahoo.com address, and send your vacation response message to victim@example.com. It will appear to come from fake_name@yahoo.com, and there will be no trace of you, your originating IP, or anything like it in the message.

You can even configure it to respond with a normal "out of the office" message to email from, oh I dunno say, @yahoo.com addresses. Not that yahoo seems to care about this.

Ta-da.