[exim] 'boolean' LDAP query...

I've setup an LDAP query like that:

    unseen = ${if eq{${lookup ldapm {user=LOCAL_AD_BIND_DN pass=LOCAL_AD_PASS ldap:///LOCAL_AD_ALIASES_DN?rfc822MailMember?sub?(&(objectClass=nisMailAlias)(cn=${quote_ldap:${local_part}}@${quote_ldap:${domain}}))}}}{}{no}{yes}}

query work (tested by hand; and if i set manually 'unseen = yes', it is
used by the subsequent router) but 'unseen' is every time 'no'.


Probably is because checking for empty result in an ldap query have soem
trouble.

How can i setup a query/condition that simply set 'yes' if the ldap query
return some output?


Thanks.

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