[exim] 5xx errors on RCPT being ignored...

It seems like I am getting 5xx errors on some outbound RCPT commands
(mostly to bounce messages), but Exim doesn't seem to take that as a
permanent error. Instead it freezes it and retries. Is there anything I
can do to make the 5xx's kill the message? Thanks. Example below...

2007-03-04 05:55:32 SMTP error from remote mail server after RCPT
TO:<recognizedseller.com@???>: host q0.netfirms.com
[38.113.168.70]: 553 sorry, that address is unknown
2007-03-04 05:55:32 recognizedseller.com@??? F=<> P=<>
R=dnslookup T=remote_smtp: SMTP error from remote mail server after RCPT
TO:<recognizedseller.com@???>: host q0.netfirms.com
[38.113.168.70]: 553 sorry, that address is unknown
*** Frozen (delivery error message)