From an administrator that works with Domino for more than 15 years I would say:
Before Domino 5 the limit was 4 Go. after Sky is the limit. but their is best practice and also performance. a database that is biger than 4 Go can give the user some performance issue. but the worsk is when a server crash. If transaction log on not activate (server document / transLog) the server will do a consitency check on the database and it will take forever to restart the server. so it is best to archive the email in those database. and use quota so the email database will not go over 4 Go. that is verry big for email. It is also a good practice to delete attachement in the mail database.
Enjoy your new task. Administering domino is a very cool Job with some god Chalenge.
These limitations are tested, known limits. Pushing Notes databases to these limits would likely have performance impacts and would have to be carefully tested.
I am not a server administrator. However, I would expect that these huge maibox sizes should be managed. In the links below, you will see the tested upper limit in R6 is 64 gb. That doesn’t mean these large file sizes are not a problem.
I would expect a more complete answer, including some best practices, from administrators on this forum. Have you searched the IBM R6 forum for related questions?
IBM R6&7 Forum.