[Exim] quoted local parts

I have a problem with addresses which arive with local parts in quotes (usually
because the sender mis-typed). I would expect these to be rejected as "Unknown
local-part" but I get an error from one of my directors and the messages are
frozen. The problem arises because exim strips the quotes and then complains
when it subsequently needs them to be there.

The director is
canon1:
driver = smartuser
domains = exeter.ac.uk
no_rewrite
new_address = $local_part@???
new_director = <next one>

When "A>N>Other"@??? is being processed I get the error "error in
smartuser ....: missing or mal-formed local part (expected word or ">") in
"A>N>Other@???".

How do I deal with this please?

Phil.
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Phil Chambers (postmaster@???)
University of Exeter