2 things-

1- you need have the location for each user in LDAP. This is defined in your authldaprc file, the value is LDAP_MAILDIR. In mine, I use the attribute MAILBOX for each account in ou=people. So my *authldaprc* config file has the following:

LDAP_MAILDIR mailbox

2- you need to tell postfix *which* user is supposed to deliver the mail. In your case, MAILADMIN.

In /etc/postfix/master.cf, you should have a line like this:

maildrop unix - n n - - pipe flags=Ru user=mailadmin argv=/usr/bin/maildrop -d ${recipient}

Dave