[Mailman-Users] Spam filtering

[Geoff Shang]

Hello,

I have two spam-related questions, one relevant to Mailman and one not. 
Apologies for the one that isn't, but I hope you will endulge this query.

A person has been spoofing Email addresses on a number of 
blindness-related Email lists this week.  I won't go into the particulars 
as it's probably of little interest to this list.  They're also using some 
quite sophisticated techniques to hide their identity and point of origin, 
and this is definitely outside the scope of this list.

My questions here are more focused at helpping list/site admins to block 
such mail.

1.  It's possible to use an IP address to block(at least temporarily) 
these messages.  If I put this IP address into a Mailman spam filter, will 
this be checked *before* checking whether or not the person is a member of 
the list?  I want to know if list admins can block these without bugging 
their site admins to do it upstream.

2.  One idea I came up with for rejecting spoofed mail is for the 
receiving SMTP server to somehow check if the sending one is an MX for the 
domain given in the From header.  Are there any obvious problems with this 
approach?  Is anyone actually doing this?  It seems so simple that there 
surely must be some reason why it's not done.

Geoff.