How I can count the number of user mailboxes I install?
To count the number of mailboxes in your site, just click on the Recipients tab and look at the status bar on the lower left corner of the screen.
The default view shows you all recipients, including custom recipients and distribution lists. If you’d just like to see the user mailboxes, click the View menu and restrict the list to user mailboxes, distribution lists, or whatever you’d like to see. The count on the status bar will update to show you only the count of what you’re looking at (distribution lists, user mailboxes, etc.).
To see the list for a specific server (if you have multiple servers), do the same thing, except expand out the server objects until you see “Server Recipients” listed and click on that.