Send From an address, but discard any incomming mail to that address, sendmail?

[Shaun Forsyth (RPM Solutions)]

Hi Guys,
    I know not strictly a mail scanner question, but its on one of our 
mailscanner servers, and could maybe something mail scanner can help with. 
Currently using sendmail with virtual users, user noreply at domain is used to 
send email from scripts on the server, the domain is listed in 
local-host-names however I cleaned up the virtual user file the other day 
and added a bunch of @domain error:nouser No such user here no the server 
wont send from that address?

I should point out that I can't simply trust the user that the script is 
running as, as the mail is being smart hosted from another server to this 
server, the access file currently has 2 lines Connect:[IP] RELAY and [IP] 
RELAY already in it.

Any one think of a way that this can be done, to be able to send from the 
address but drop, reject, discard the mail coming back in.