[Mailman-Users] How to accept mail from a single IP / DNS name only for a given list

[Emmett Perdue]

1st, forgive me if this has been answered before. I have searched high  
and low and can not find an answer to my question.

How can I setup a list so that mail can be accepted ONLY from 1 IP  
address? As an example I have a list named abc at 123.com and it is setup  
as an announce list only accepting mail from 1 user with an address of bob at 123.com 
.  How can I set this list up so that even if the mail appears to come  
from bob at 123.com the email will post to the list ONLY if bob at 123.com's  
email came from bobspc.123.com which has an an IP address of  
123.456.789.246

Thanks!