[Exim] How to use director and receiver_try_verify together?

Hi, all

I am using Exim 3.35 under Debian. In my exim.conf, I have follow setting in
the director handles:

lamsgroups:
driver = smartuser
new_address = lamsgroups@???
no_verify_recipient
no_verify_sender
suffix = ".*"

So that all emails have the format xxx.yyyy@??? can redirect to
the one real email address lamsgroups@???
I use this way to create many discussion groups and all belong to one email.
then I use my own app to pick the emails and deliver to the groups. It works
fine. Now I face another problem - my exim server receive hundreds of spam
and virus per day. And lots of these email just send to a fake email address
like 20031015122326@??? and cylew6@??? I try to
block these emails by using receiver_try_verify = true to block the spam
emails. But once I do it, exim block all my groups' emails too!

So my question is, does any way I can make receiver_try_verify = true and
still allow my lamsgroups director working?

Cheers,
Tao