This is a good article in technet (again, 2007 but the explanation applies):
http://social.technet.microsoft.com/Forums/en-US/exchangesvradmin/thread/af35666e-16a4-43ca-b7be-1dfffefaf8f8/Quoting here:
Yes, the max value for each type is 32767
By default:
· Named Properties Quota – 16K (16,384)
· Non-MAPI Named Properties Quota – 8K (8,192)
· Replica Identifiers Quota – 8K (8,192)
“Do not increase the quotas to the hard limit of 32,766 entries. If you must increase the default quota for either named properties or replica identifiers, you should identify the root cause for the situation and not allow the named properties or replica identifiers to reach the maximum limit.” ------------------<Named Properties or Replica Identifiers Are Depleted for An Exchange Database>
Another workaround besides increase the quota is, to distribute the fewer mailboxes per database, so the warning or error would take more time to occur
However, the best method to eliminate the quote warning and error events is, dump the named Properties table from Information Store to check the properties. Figure out which application they are coming from and get that changed.