TNEF File Help

[Joomy]

Dear All qmail Gurus,

I got this error in my qmail outgoing log. (I'm using qmail 1.03 on Redhat
6.2)

delivery XXXX: failure: Seems_not_to_be_a_TNEF_file / ...... / ........

and sometime

delivery XXXX: success: Seems_not_to_be_a_TNEF_file / ...... / ........

What is the TNEF file ? Is it some format from ms outlook ? (sorry for my
stupid)
What should I do ?

THX.
Joomy.