Exchange WinMail.DAT

Frequently using a Mac for my desktop I have occassionally received messages with or without original attachments but in my Apple Mail.app program I see a 'Winmail.dat' file attached. There is no default program to open it but sometimes there is valuable information inside that file. This often afflicts other receiving mail clients as I've heard it happens in Thunderbird and Eudora sometimes too.

The cause is that the sender is using Outlook and has chosen Outlook's Rich Text as the editing format. In my experience, the sender is also on MS Exchange. Of course, the sender should probably use a more standardized editor, either plain text or HTML but how would they know what they're doing, particularly if the vast majority of their recipients don't mention the problem.

If you're an Exchange administrator, probably the easiest way around it is to simply disable the 'Exchange rich-text format' on the Exchange Server itself. Below is a screen shot from one that we administer running Exchange 2007. Open the Exchange Management Console/Org. Config/Hub Transport/Remote Domains/Format... tab, and select 'never use' on the Exchange rich-text format section.