From past few days, Some of my users users were getting these “winmail.dat” attachments in Lotus Notes and were unable to open them and usually the sender is always from Mircosoft Exchange/Outlook User.
After some googling, I was able to sort it out.
Open Lotus Domino Administrator , goto SERVER , then SERVER CONSOLE, , and in the DOMINO COMMAND , issue the following commands , paste following two commands , one at a time . . .
set config TNEFKeepAttachment=1tell router update config
The problem is that Outlook is tunneling rich text formatted information in an attachment through the Internet using a proprietary format (by Microsoft), rather than MIME (an Internet standard).
Microsoft opened up the format so other vendors could read the content, and IBM and other vendors have included that ability in later patches.
For more info, please read the below article from IBM.