Question : Exchange 2003, Outlook 2003, Outlook Express and winmail.dat

I have 3 Exchange servers, 1 Ex2003 server in the US, 1 EX2000 server in US, and 1 Ex2003 server in Asia.

Most US users are using Outlook 2003, many Asia users are using Outlook Express (not sure of the version).  

I am in the middle of migrating a good number of Asia users from the old Exchange 2000 server to a new Asia Exchange 2003 server.

My issue is that SOME users that have been migrated to the new Ex2003 server AND using Outlook Express are now receiving emails where the attachments have been converted to winmail.dat.

After reading a great many articles, I double checked one of the users that was SENDING the emails, and their Outlook settings DO not include RTF or use Word as the editor.  To take my testing one step further, I created an account on the old Ex2000 server, then migrated it to the new Asia Ex2003 server; then using Outlook Express, I had the SENDER send me the same email that he was sending to Asia.  Wouldn't you know it, the email showed up just fine.

So, i am convinced that it has something to do with the Exchange servers "TNEF"ing the emails during transport, based on the recipients mailbox, but do not know where to go from here.

The issue    

Answer : Exchange 2003, Outlook 2003, Outlook Express and winmail.dat

check this:
Winmail.dat attachments are included in received e-mail messages in Outlook
http://support.microsoft.com/kb/278061