Sounds like a mailcap problem? You can tell your client how to open every file imaginable. With mutt, I use an ascii preview of the image so I can screen out signatures and then when I open an image, it opens with an image viewer. I have websites, pdfs, doc, xls files all dumped to a text preview mode, then open them in an appropriate viewer if I feel the need further investigation. Turns out most of the time, those emails boil down to pictures you don't need (like logos and b roll headers) and a few words. Most of the joy of terminal email for me is filtering out all the cruft and being left with words.