Is this going to be a permanent solution or will you eventually have access to their existing LDAP?
This is probably a bit over my head but one solution you could try is:
1. csv file your desired contacts
2. create a generic zimbra account
3. import the csv file into that accounts Contacts folder
4. Share the contacts folder to the rest of the company
Now a couple things I am not sure of:
1. Will a TO: field auto populate from a Shared Contacts folder?
2. Is there an easy way to add 20,000 users to a shared list?
Just a thought. Will have to see where it goes.
"Let's look at this from a standpoint of "Status". What exactly, on the Space Craft, IS working?"
-Flight Control, Apollo 13