[Exim] mesages frozen due to unknown local-part

Recently spam has been sent to my mail server directed to email
addresses with unknown local-parts. These messages get frozen and the
postmaster is notified. Is there no way for messages sent to email
addresses with unknown local-parts to be dismissed automatically?

Here is a sample of the warning sent to postmater:

Message 1AreNq-00009F-00 has been frozen (delivery error message).
The sender is <>.

The following address(es) have yet to be delivered:
unknownuser@???: unknown local-part "unknownuser" in domain
"domain.tld"

Cheers