Filtering/ blocking forged emails

[Nandini Mocherla]

I am new to postfix/SpamAssassin and thinking for a way to block the 
email address which does not come from that domain. For example, if 
someone with a @xxx.com email sends to a list it must come from a server 
in the xxx.com domain else it should be rejected.  Is it possible to do 
this? As there is every possibility that spammers can also send with 
real user's id and I am planning to have a check that would  be able to 
compare the From: and the Message-Id domains to check for spoofed 
messages coming in from an open relay. Its just an idea to eliminate 
every possible attack.  As i don't have much experience with postfix, 
just installed/configured a couple of days ago any suggestions in this 
regard will be highly helpful for me.  I have also read some whre about 
Sender Score Certified support in SpamAssassin.  But not sure how this 
works? Will it check the senders from address and compare it with the 
domain?