[EXIM] accepting bad addresses?

I'm using the smartuser driver as follows:

punt:
driver = smartuser,
no_verify;
new_address = ${local_part}@???,

I've gotten a few frozen messages like this:

1998-05-21 08:10:09 0ybNTC-0004XU-00 == "FAILURE.DURING FTP OF TOPXXX REPORT"@??? D=punt defer (-10): <failure.during ftp of topxxx report@???> - bad address generated by punt director: missing or malformed local part (expected word or "<")\n
1998-05-21 08:10:09 0ybNTC-0004XU-00 Frozen

How do I avoid this? I'm using exim-1.82.


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