The setup is exim4 and amavis-ng and SMTP transport.
Everything works fine if a virus is found. Then the Notifiers get
their email, however, if there is no virus found exim4 rejects the
message that is returned from amavis-ng because DATA is sent
without sending a RCPT TO before.
I have added one line in accept_message() before sending DATA:
which sends the original recipients.
This is a quick hack. it seems to work but may break other things.