If you install an Exchange Server computer in a large site, when the server attempts to send an e-mail message over an installed connector, such as the Internet Mail Connector in Exchange Server 4.0 or the Internet Mail Service in Exchange Server 5.0, the server may run low on or run out of Entity Control Blocks (ECBs).
The following events may be logged in the Microsoft Windows NT application event log:
Event ID: 248
Source: MSExchangeMTA
An internal MTA error occurred. An attempt has been made to process too many entity control blocks (ECBs) by a single thread. Number of ECBs processed: 10. [MTA DISP:ROUTER 14:331] (14)
Event ID: 41
Source: MSExchangeMTA
There are too many concurrently connected entities. There are no free entity control blocks (ECBs) available. There are currently %1 ECBs configured. [MTA DISP:ROUTER 12 119] (14)
Message delivery may also be slow.