Email on iPad and iPhone shows attachment as winmail.dat

Some of the users in our organisation have reported that when sending email messages with attachments to external users they receive a winmail.dat file instead of the original attachment.  I have read many blog posts and articles about configuring Outlook to send using plain text or HTML instead of RTF (Rich Text Format).  However, this didn’t solve the problem for me as the attachments were still being received as winmail.dat when sent as HTML or plain text.

My investigation led me to notice that the recipients are contacts in our Exchange environment. For contacts Exchange allows you to configure whether or not to use RTF.  Modifying this option for the contact worked for me, and here are the steps required:

1. Open the Exchange Management Console

2. Expand Recipient Configuration and select Mail Contact

3. Right-click on the contact and select Properties

4. On the General tab set the Use MAPI rich text format option to Never

5. Click OK

Now attachments sent to this contact are no longer received as winmail.dat