using OpenLDAP's ldapsearch, how to get mailaddresses from Exchange
(at least the first 1000 entries.. AD has a searchlimit using ldap://)

ldapsearch -H ldaps://<remotehost>:389/ -x -D <yourlogin@yourdomain.com> -W \
    -b <your-base> proxyaddresses

Someone found this via google btw, so go google for more rather than
ask me :-)