Myck...
Use the plain text setting... if you want a mixed set of sending options, goto the client contact page, double click on the clients email address, you should get a email property box for just that client, there is a pull down for the internet format, select plain text only...
If this does not solve the probem here are 2 other options...
WMDecode
http://www.biblet.freeserve.co.uk/Program using a simple drag and drop procedure to view winmail.dat contents
TNEF's Enough
http://www.joshjacob.com/mac-development/tnef.phpMacintosh program to decode winmail.dat TNEF attachments
The last suggestion is you already have MS products running... Windows Live has as part of it's package, Skydrive... 25 gigs of posting space and up to 50 megs per file...
you can post images there for your client to see and download... and best of all, it's free!!!
www.live.com another program in the package is Window Live Gallery... free photo database tool and you can upload directly to skydrive from there...
HTH...
Ed