A customer of mine mentioned that they were told by a vendor that Microsoft recommends that Exchange databases should not be more than 200 GB. I was not aware of this being a recommendation by us. Then I found the following link:
Planning Disk Storage
There we do say the following: "Because the maximum recommended database size in a CCR environment is 200 GB, the server should host no more than 180 mailboxes per database."
That 200 GB recommended limit is only on servers that are doing CCR. The 180 mailboxes limit was based on each mailbox having 1 GB limits. We actually recommend that you not have database larger then 50 GB. In fact, if you run one of the Microsoft Exchange Server Analyzer tools we will may throw a warning if the server has databases that are 100 GB in size:
The Exchange Database exceeds 100 GB in size
We still have a 16 TB limit on the size of an Exchange database, but we don't recommend that you have databases that large if you need to backup and recover them in a timely manner. Maybe a company's SLA, hardware and architecture allows you to run larger databases. We however have found that most companies prefer to be able to get there databases recovered in a timely manner, so 50 GB might be the largest that they can handle.
Be sure to consider how long it would take to backup, restore, or run maintenance on your databases before letting them grow to an unmanageable size.