Run telnet mail.realdomain.com 25 from command prompt
You get:
220 server.domain.com Microsoft ESMTP MAIL Service, Version: 5.0.2195 ready at Tue, 20 Apr 2004 17:37:15 +0200
Type helo
Type mail from:<tester>
Type rcpt to:<abuse@somedomain.com>
If you get:
550 5.7.1 Unable to relay for abuse@somedomain.com
It's O.K
Read how to use and test spamhaus.org RBL in Exchnage
