[exim] Exim Config and Space characters Question

Hi Everyone,

I have what is probably a simple question. Unfortunately, I cannot find
an answer.

In a ${lookup{key}lsearch{file}{string1}{string2} directive, how do I
pass in a space character for one of the {string1} or {string2} values?

This is my transport_filter line:

Spamcheck:
# If user exists in /etc/passwd, pass username as argument
transport_filter = /usr/bin/spamc -x
${lookup{$local_part}lsearch{/etc/passwd}{-u $local_part}}

This is the error I get:

Expansion of "${lookup{$local_part}lsearch{/etc/passwd}{-u" from command
"/usr/bin/spamc -x ${lookup{$local_part}lsearch{/etc/passwd}{-u
$local_part}}" in transport filter failed: missing } at end of string

Can someone advise me of how to fix this? Thank you very much for the
help!

Jae