Consider a scenario where you are publishing a SMTP Server that uses TLS on Forefront TMG 2010, in such scenario TMG resets the connection to the SMTP client when the SMTP server closes its connection to TMG with a TCP FIN packet. This behavior can cause some specific SMTP client applications to report that message delivery failed even though messages are sent correctly. In this scenario you also will see the following entry on the Live Logging: Incoming SMTP Server    0x80074e24 FWX_E_CONNECTION_KILLED. This problem is documented for ISA Server 2006 in KB 959312. Recently we also experienced the same issue with TMG and the script from KB 959312 fixed the issue. After running this script on TMG you should see the message below on your command prompt windows (which should be opened in privileged mode):

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After this change such behavior should go away…and yes, we will update this KB to include TMG.

Note: only run this script on TMG if you are experiencing exactly the same behavior as explained in KB 959312.