Have PostFix check the LDAP server when it receives an email. If the recipient exists in the LDAP server, forward email on to main mailserver. If not, discard the email. I don't want a script file that runs every hour to load a new list of users into the list.

Current Situation:
email addresses are: first.last@domain.com
I got PostFix checking the LDAP server when it receives email with the changes:

alias_maps: ldap:ldapsource1
ldapsource1_server_host = ldap.domain.com
ldapsource1_search_base = ou=users,o=domain
ldapsource1_query_filter = mail=%s

When I check the log and packets, I see that PostFix queries the LDAP server. The LDAP server returns with the maildrop attribute information. Then PostFix gives me an error saying, "unknown user: 'first.last'"

I don't know where to troubleshoot from here. I'm guessing maybe the user is missing from the alias database, maybe? Is there anyway I can take a peek into the alias database to see whats in there? I run the 'newaliases' command and 'postalias /etc/alias' command and it doesn't seem to update the 'alias' file in '/etc' Any ideas, hints, clues, solutions, suggestions, or anything that might help me out?

Thanks in advance.