XCON: MTA Doesn't Start, Event IDs 9228 and 4300

The Microsoft Exchange Server message transfer agent (MTA) may not start; one or both of the following event ID's will be seen in the event viewer:

This is caused by an inadequate number of control blocks allocated to a transport stack. In the above error message, the "network type 2" refers to TP4 protocol. Two control blocks were requested; however, there is one allocated control blocks. The content of this error message may vary, dependent on the mis-configured control blocks for the network type.

WARNING: Using Registry Editor incorrectly can cause serious problems that may require you to reinstall Windows. Microsoft cannot guarantee that problems resulting from the incorrect use of Registry Editor can be solved. Use Registry Editor at your own risk.

For information about how to edit the registry, view the "Changing Keys And Values" online Help topic in Registry Editor (Regedit.exe) or the "Add and Delete Information in the Registry" and "Edit Registry Data" online Help topics in Regedt32.exe. Note that you should back up the registry before you edit it.

To correct the problem, do the following:

1. Start Windows NT registry editor (Regedit or regedt32).
2. Modify the following value to 0x2

         HKEY_Local_Machine\System\CurrentControlSet\Services
         \MSExchangeMTA\Parameters\TP4 control blocks: Value 0x2

There must be at least two control blocks allocated to TP4 in the registry. This is true regardless of whether TP4 protocol is used or installed on the server.

The default registry value for TP4 is 0x14H or 20 Decimal.

For information about the limit on the number of allowed socket control blocks for TCP and TP4, please see the following article in the Microsoft Knowledge Base: