Why am I receiving winmail.dat attachments?
Users may receive this file as an attachment instead of the regularly attached file under these very specific circumstances:
The sender is using Outlook for Windows The sender has a contact record for the recipient enabled to use Rich Text or his default settings are set to use Rich Text The recipient is not using Outlook for Windows
Recipients of these files must use third-party software to decode the . . .
Continue Reading: Winmail.dat