Hello
As file exchange calculator I have three tier with number of tier as below

as My understand then number of tier 1 + 2 + 3 = number user per one database (105 + 23 + 1 = 129) .I want enable mailbox auto but I have problem is how to know one database full tier 1 or 2 or 3.
example : I have three database MB01,02,03 .Now when add one user tire 1 how to know is tire 1 which database MB01,02,03 can add and not full (=105)
Please anyone share help me best way to enable mailbox auto assign to database
Thanks