It doesn't return the mail, just a brief bounce message, and that can 
be turned off.
As I mentioned, it can be good to let legitimate people know their 
email didn't go through,
but it's up to the admin to determine which way they want it.

John

At 02:07 PM 11/1/2006, you wrote:
>"LISTSERV site administrators' forum" <[log in to unmask]>
>wrote on 11/01/2006 01:03:09 PM:
>
> > It can be configured not to return bounces.  For non-listserv
> > installations, returning bounces does perform the useful task of
> > informing legitimate people that their email did not get through and
> > they can then take appropriate action.  It's possible to mount a
> > reverse attack, i.e. have some poor unsuspecting individual get
> > thousands of real bounces because their email address was used in one
> > or more large spam mailings.
>
>Returning bogus mail is just plain wrong.  The trick is to *NOT* accept
>it.  This requires evaluating messages DURING the connection, before
>returning "250 message accepted".  Any of the spam filters based on
>sendmail's milter interface can do this.  Other MTAs may be able to do
>this as well.  Closing the connection and then evaluation is going to
>guarantee either lost mail or backscatter spam.