I have an SBS2008 server with all the latest updates, Exchange Server 2007 service packs and post service pack roll ups.
When a user on a MAC or a PC sends a PDF file from their Exchange email address to any user, it comes as a winmail.dat file. Some users are also experiencing this with attached spreadsheets.
The Windows PC is in the domain or outside the domain and using Outlook
The MAC is not in the domain. The MAC is using MAC Mail