Configure sendmail to reject mail for unknown users?

[Tim Alberts]

Les Mikesell wrote ..
> If the server isn't set up to relay to a hub machine or
> forward via mailertable, then it should automatically
> reject any address that is not a local account.  Maybe
> you have PostmasterCopy enabled.  Look in sendmail.cf
> to be sure that 
> #O PostmasterCopy=Postmaster
> has the leading # to comment it out.  I've forgotten the
> sendmail.mc invocation that would enable it but these
> days you probably don't want it on.
> 
> Virtusers is mostly useful if you forward or accept for more
> than one domain or wish to appear to.

That line is commented (#).