XCON: ECB Usage Count Events Appear with Large Directories

SYMPTOMS

When you send a message to a Microsoft Exchange Server computer with a directory that contains an extremely large number of mailboxes and distribution lists, numerous 9405 events may appear in the event log with a source of MSExchangeMTA. These events indicate that the problem is related to the number of entity control blocks (ECBs) that are being used. This problem can also occur when you perform directory replication with a directory that contains an extremely large number of mailboxes and distribution lists.