need help blocking emails to non-existent users

[Steve Campbell]

Joey Marino wrote:
> I am currently running a mailscanner box on centos using sendmail that 
> relays to my exchange server.  I am trying to block email to 
> non-existent users at the smtp level on the MX. I understand I have to 
> somehow update sendmail with existent users in the active directory 
> possibly using ldap. I can't seem to find any good documentation on 
> how to do this. Many entries in the archive point to 
> http://www.mailscanner.info/serve/cache/270.html but this doesn't 
> exist anymore. I also found a sketchy bash script at 
> http://the-jer.spaces.live.com/blog/cns!E4FBBD09FA146AF!128.entry 
> <http://the-jer.spaces.live.com/blog/cns%21E4FBBD09FA146AF%21128.entry> 
> but I don't like this approach either. I want to do all the work on 
> the gateway. Can somebody point me to some good documentation or a 
> healthy script that I could use to accomplish this?
>
> -- 
> Joey Marino

I run MimeDefang for this singular purpose, although MD will do lots 
more if I ever need the extra functionality. I use the  
md_check_against_smtp_server function and throw away the mail 
immediately if it returns an invalid recipient.

Steve Campbell