[Exim] LDAP Lookups

Our typical "watered-down" LDAP entry looks like this:

dn: uid=jkezar + cn=Joseph Kezar,ou=People,o=DOC,c=US
cn: Joseph Kezar
uid: jkezar
mail: joseph.kezar@???

The user jkezar is a local account on the mail server. How can I get exim
to deliver to jkezar when the email is addressed to
joseph.kezar@????