[exim] LDAP, posixGroup and mailing lists

I'm slowly getting there and getting used to working with exim. I'm
rather stuck at the moment trying to work out how to use posixGroup
entries in LDAP to store mailing list members. I can lookup the uids of
the members using the following line

data=${lookup\
    ldap{ldap://localhost/dc=jolt,dc=co,dc=uk?\
        memberUid?sub?(mail=${local_part}@${domain})\
    }\
}\

From this stage, how do I perform additional lookups, using these uids
fetched with the above query to lookup the e-mail addresses of the users?

James

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