[Exim] Rumplestiltskin attacks anyway to combat them?

I have a mail gateway running 4.34 clamd and spamassasin with a smart_route
to a internal exim box. I am getting rumplestiltskin attack to the point
that I can honestly say that over 4k of messages that hit the gateway get
bounced with a 550 unknown user or at least try till the timers on frozen
messages get them in 5 minutes. Has anyone found a good way to combat this
problem. I have googled on "rumplestiltskin attack" and for a few hacked
perl scripts nothing else really. I know this was brought up in here a few
months ago but google doesn't seem to index the archives very well.
I wish I could think if a way to check the internal boxes user list before
the ext. gateway passes the message on. I turned on verify_recipient but
that did not seem to change anything.