Tarpitting

Tarpitting is a function of Exchange 2003 and later which prevents directory harvesting and NDR attacks. It throttles Exchange’s processing of incoming messages. The interval can be viewed by running the following:

Get-ReceiveConnector | Select Name,Tarpitinterval, Maxacknowledgementdelay

For troubleshooting purposes, the interval can be changed by running the following:

Get-ReceiveConnector | Set-Receiveconnector -tarpitinterval 00:00:00

The MaxAcknowledgementDelay setting is used by Exchange when receiving messages from email applications that don’t support Shadow Redundancy. Shadow Redundancy allows for message redundancy during the entire transport process between Exchange 2010 Hub Transport servers.

http://technet.microsoft.com/en-us/library/dd351027%28v=exchg.141%29.aspx

http://technet.microsoft.com/en-us/library/cc526521.aspx