[TriLUG] simple mail filter. best option?

[Aaron S. Joyner]

Cristobal Palmer wrote:

> I have a site, bar.com, that will be receiving mail from clients such
> as foo and baz who have their own domains, foo.com and baz.com.
>
> I want to set things up such that mail to foo at bar.com only gets
> through if it came from *@foo.com, likewise mail to baz at bar.com should
> be dropped if it didn't come from *@baz.com.
>
> What's the _best_ way to do this if I'm using postfix? Something
> directly in postfix? Procmail?
>
> TIA,
> CMP
>
Check out smtpd_sender_restrictions, you'll probably want to add a 
check_sender_access table like this:
smtpd_sender_restrictions = check_sender_access 
hash:/etc/postfix/incoming-domains

which points to a file with entries like these:
foo.com      ok
baz.com      ok

You'll also need to makemap hash /etc/postfix/incoming-domains to create 
/etc/postfix/incoming-domains.db for the above example to be acceptably 
fast (I think it'll work if you don't, just at a great performance peril).

More details can be found in the postfix documentation, here:
http://www.postfix.org/postconf.5.html#smtpd_sender_restrictions

You'll probably want to do some other smtpd_sender_restrictions, and if 
you've already got several of them add the one above in the style of the 
others.  Rejecting based on the MX might not be a bad idea either, as 
it'll cut down on spoofing at the expense of a dns lookup for every 
connection.  If you can afford to do that depends on how likely someone 
is to spoof mail to you maliciously, and what volumes of mail you're 
talking about.

Please post back if you have further questions,
Aaron S. Joyner