For the smoothest deployment possible, you should go through the following four phases:
This gives you access to the Administration Console, with one administrative account, one organization, and one server.
Add a small group of users and possibly add additional administrators. Set up your service
Using LDAP Discovery, Add your remaining users and domains, and set the filter configurations and access levels as required.
On-going support of your users and servers. This may require adjusting filter settings, managing users and domains, and adding new or configuring existing email servers.