How can he open the ATTACHED winmail.dat file using Outlook?
Conforme listado neste Microsoft KB , " Os dados em um arquivo winmail.dat não é utilizável "
Email received from a sender using Outlook includes a Winmail.dat attachment
CAUSE
The Winmail.dat file is used to preserve Rich Text formatting. Outlook uses it when sending a Rich Text-formatted message. During transport, the content of the message may be changed, preventing the receiving client from being able to read the formatting instructions. In other cases, the receiving client does not use or recognize the winmail.dat file.
RESOLUTION
The data in a winmail.dat file is not usable. To resolve this issue, ask the sender to re-send the message in plain text format. The following methods can be used by sender to prevent sending Rich Text messages encapsulated in the Transport Neutral Encapsulation Format (TNEF).