[X-Apps] Windows users can't receive attachments

[Ken Rossman]

>> I have a problem at work when I email an attachment to computers
>> running Windows, they can't open my PDF or JPEG attachments.
>> It works fine running OS 9, but not with 10.2. I've tried OS X's
>> mail program and Eudora, but I get the same results. Mac users
>> can receive and open the attachments with no problems.
>
> Specify MIME encoding (AppleDouble in Eudora). You're probably using 
> Binhex, and the PC users are probably using Outlook.

Where does one specify MIME encoding in Mail.app?  I've missed this
in the preferences...