I have a Barracuda Spam firewall that is setup to perform LDAP lookups against AD to ensure that recipient names are valid. However, that ability has somehow stopped and I'm not sure why. Specifically, it was sending these queries to our Exchange server at port 389 (I believe). At first I thought something must have gone wrong with the Barracuda and so I called tech support, however, after I was unable to telnet to port 389 and 3268 from within my network, I was told that the problem was with the Exchange server.
What do I need to change to get this Exchange server to respond to LDAP requests (or telnet connections on those ports)?