Quoting Christopher Glanville:
> server_condition = ${lookup{$1}lsearch{/etc/exim/passwd.client}{${if eq {$value }{$2}{yes}{no}}}}{no}}
Besides the issues that Philip pointed out, you will probably act as an
open relay with this config. You will authenticate anybody with an
invalid username (i.e., one that is not in passwd.client) and a single
space password. This is a somewhat common error (and there is a warning
in the wiki about that, IIRC).