This article applies to:

• MailMarshal Exchange 5.3.X
• Exchange 2007 

Symptoms:

• Error: "Invalid TNEF file – winmail.dat>"
  
  Unpacking TNEF file.
  Failed to load tnef objects. ReadExact: read only 1 bytes requested 4
  TNEF file unpacking *FAILED*.
  Event - Unpack for BA001387DD.0013A681.mml caught exception <Invalid TNEF file - winmail.dat>
  
  
• Affected messages are deadlettered by MailMarshal Exchange

Possible Cause:

• This error can occur when differing versions of Exchange 2007 are used within the same domain (for example Exchange 2007 SP1 Roll-up 6 and Exchange 2007 Roll-up 7).
• The winmail.dat file is actually corrupt - this is not a MailMarshal Exchange fault.
  

Possible Workarounds:

• It may be possible to resolve the problem by ensuring all Exchange 2007 instances within the domain/organization are on the same service pack level.
• With previous TNEF compatibility issues, Microsoft has recommended not using Word as email editor.

Notes:

There are other possible causes of TNEF unpacking errors. This error is specific to the environment named.