This INI variable will cause the Router to check each message to be delivered, and verify that the current mail file size plus the size of the current message is less than or equal to the size specified. This check assumes that the file might need to be extended to make space for the message being delivered, and does not account for any unused space in the database that might be able to accommodate the message. Note that all deliveries on a server with this variable enabled will need to be made to databases less than the size specified.

IMPORTANT:
All deliveries on a server with this INI variable enabled will need to be to databases less than the size specified; there
are no exceptions. Since there are no exceptions, this is not recommended for mail servers hosting mail files which
should have no limits, for example, your CEO's mail servers.