[exim] email notification

Hi all

I would like to ask you guys if you can help me with this fetchmail problem.

I have setup fetchmail to fetch a multidrop account, Exim is setup to
reject all unknow users. Error 550.

When fetchmail fetch the mail I can see it reject unknow e-mail with
error 550 and flush the mail, but know it does not send out a notice to
the sender.

Any one had the same problem, I would really appriciate any help

Brent Clark