Document failure?Gmail?

Hi. I'm having trouble with a client who can't read my Word docs (created on Mac, but with suffix .doc which always work with everyone else, whether using pc or mac). He tells me he has had similar trouble with someone else. Could it be Gmail (the emailer he uses), so making us use googledocs to exchange documents? Anyone any ideas how to resolve this problem? First thing, I guess, is to try using a different email provider.