How would you design this LDAP schema

We are looking at building a ldap directory for mail servers.

We are looking at building something similar to what I have below.  I am looking for an idea on how the schema would be designed (LDIF format is fine).

We would have multiple companies (customers) each with 1 more more domain names.  Under the domain name would be 1 or more email addresses (primary and 0+ aliases).  

So we may have 50 companies with one or two domain names with 15-150 users under each domain name and 1 primary email address with 0 - 10 secondary email addresses.  We want to be able to query at the top of the tree for an email address (when querying, we do not care what company it belongs to and what domain name, we will simply look in the directory to see if the email address exists).

Is it possible to put UID's in groups by domain and company like this and still search for "UID->Email" accross all groups?

What would the schema look like to handle this?

Top of Tree (Our dc;dc?)
     Company (Customer) name
          Domain Name 1
                  User ID 1
                      primary email address
                      alias 1
                      alias 2
                      alias 3
                      ...
                  User ID 2
                      primary email address
                      alias 1
                      alias 2
                      alias 3
                      ...
                  User ID 3
                      primary email address
                      alias 1
                      alias 2
                      alias 3
                      ...
          Domain 2
          ...
                  ...