Like most other application software, Yahoo also has different versions for different platforms. Not all versions are compatible with all platforms such as the IOS, Mac etc. The same holds good for devices as well as to whether the user is accessing Yahoo on a mobile platform or on a web platform.Users can refer to the rich set of documentations and illustrations on the customer support portals hosted online, or connect to the customer support team of Yahoo to be aware of the correct application version for each platform. Yahoo express not working on Mac may be a versioning problem wherein the particular version may not be compatible.